Mike had woken up before the alarm, Sarah warm and soft against him, sunlight already filtering through the sheer curtains of the beach house. He'd kissed her shoulder, gotten a sleepy murmur in response, and slipped out of bed to make coffee.

At thirty-five, Mike still felt good in his skin. He ran regularly, played basketball on weekends, had kept the body he'd had at twenty-five with only slightly more effort. The gray threading through his dark hair was minimal, distinguished rather than aging. He caught women looking sometimes—not often enough to be vain about it, but often enough to know he hadn't completely disappeared into married invisibility.

Not that he was looking. He had Sarah, who at thirty-three was still the most beautiful woman he knew. Smart, funny, successful in her own right as a marketing director. They'd been married for five years, together for eight, and if things had settled into a comfortable routine, well—that was what happened. That was adult life.

The plan for the day was simple: drive into the city, pick up Sarah's younger sister Mia and her friend Tilly, bring them back to the beach for the day. The girls had rented a place nearby for the summer—some shared house situation with a rotating cast of twenty-somethings, and Sarah had been missing her sister.

"It'll be fun," Sarah had said when she'd suggested it. "We never get to see her anymore."

Mike had agreed easily. He liked Mia. She was smart, irreverent, had Sarah's humor without Sarah's caution. And he'd met Tilly once or twice at family things—blonde, pretty, one of those girls who seemed to collect friends and adventures effortlessly.

They'd left the beach house at nine, Sarah in the passenger seat scrolling through her phone, Mike driving with the windows down and music playing. The conversation had been easy—work gossip, plans for dinner, whether they should try that new restaurant everyone was talking about.

The city was an hour away, and they'd arranged to meet the girls at a coffee shop near their summer rental. Mike found parking, and they walked the two blocks in comfortable silence, Sarah's hand finding his.

Mia was waiting outside, and when she saw Sarah, her face lit up. "Finally! I'm dying in this heat."

Sarah hugged her sister, and Mike registered—not for the first time—how much they looked alike. Same dark hair, same sharp cheekbones, same expressive eyes. Mia was younger, obviously, still had that twenty-three-year-old glow, but the resemblance was striking.

"Where's Tilly?" Sarah asked.

"Inside getting us coffees. She'll be out in a—oh, there she is."

The door to the coffee shop opened, and Tilly emerged carrying a tray of drinks. She was wearing a sundress—white, simple, the kind of thing that looked effortless but probably wasn't. Her blonde hair was pulled back in a ponytail, sunglasses pushed up on her head.

"Sarah! Mike!" She distributed coffees with easy efficiency, then hugged Sarah. "Thank you so much for doing this. We've been dying to actually get to the beach instead of just living near it."

"Of course," Sarah said warmly. "We're so glad you could come."

Tilly turned to Mike, and he registered—really registered—how pretty she was. Not in the abstract way you notice that a friend's friend is attractive, but in a more immediate, physical way. She had the kind of face that cameras loved—symmetrical, expressive, with a smile that seemed genuinely warm rather than performative.

"Hey Mike," she said, leaning in to hug him.

It was a casual hug, the kind of greeting you'd give anyone. But Mike was suddenly, acutely aware of her body against his—the press of her breasts, the smell of her perfume, the warmth of her skin.

He stepped back quickly, probably too quickly. "Good to see you, Tilly."

If she noticed his awkwardness, she didn't show it. Just smiled and took a sip of her coffee.

They piled into Mike's SUV, Mia claiming the front seat, Tilly and Sarah in the back. The drive back to the beach was filled with chatter—Mia and Tilly talking over each other about their summer house, the people they were living with, the parties they'd been to.

Mike half-listened, focused on driving, occasionally catching Tilly's reflection in the rearview mirror. She was animated when she talked, hands gesturing, face expressive. At one point she caught him looking and smiled, and Mike quickly returned his attention to the road.

"So what's the plan?" Mia asked as they got closer to the beach house.

"I figured we'd drop our stuff, change, and head straight to the beach," Sarah said. "We can grab lunch there, make a day of it."

"Perfect," Tilly said. "I've been working on my tan but the roof of our house is not ideal for it."

"You're plenty tan," Mia said, poking her friend's leg.

"There's no such thing as plenty tan."

They arrived at the beach house, and Mike helped carry the girls' bags inside. They'd packed light—beach bags, towels, a cooler that Tilly had apparently filled with "essentials."

"The bathroom's upstairs if you want to change," Sarah told them.

Mia and Tilly disappeared upstairs, and Sarah went to the bedroom to change into her suit. Mike grabbed his swim trunks from the drawer and changed in the bathroom, trying not to think about the fact that Tilly was somewhere in this house taking off her clothes.

When he emerged, Sarah was in the kitchen packing their own cooler. She was wearing a one-piece—navy blue, practical, flattering in an understated way.

"You look great," Mike said, coming up behind her and kissing her neck.

She smiled and leaned back into him. "Flatterer."

"Just stating facts."

Mia came down first, wearing a black bikini and denim shorts. "Tilly's still getting ready. You know how she is."

Sarah laughed. "Some things never change."

When Tilly finally appeared, Mike was loading the car and didn't see her until she walked past him to put her bag in the trunk.

The bikini was white—stark white against her tan skin. It was a triangle top and bottoms that tied at the sides, simple and somehow more revealing for its simplicity. Not inappropriate, exactly, but definitely designed to be noticed.

Mike noticed.

"Ready?" Tilly asked brightly, and Mike realized he'd been staring.

"Yeah," he managed. "All set."

The beach was a ten-minute drive, and they found parking easily. The walk down to the sand involved navigating the wooden walkway over the dunes, and Mike found himself behind Tilly, watching the way her hips moved, the way the white fabric of her bikini bottoms shifted with each step.

Stop it, he told himself firmly. She's twenty-three. She's Sarah's sister's best friend. Stop.

But he didn't stop looking.

Finding a spot was easier with Mia and Tilly along—they just claimed a section of relatively empty beach and started setting up. Mike drove the umbrella into the sand while Sarah spread out towels. Mia was already pulling out sunscreen, and Tilly was adjusting her bikini top in a way that drew Mike's eye despite his best efforts.

They settled into easy beach rhythm—Mia and Sarah immediately started catching up on family gossip, Tilly stretched out on her towel with a contented sigh, and Mike tried to focus on literally anything except the way Tilly's body looked in that white bikini.

He pulled out a beer from the cooler. It was barely eleven, but vacation rules applied.

"Ooh, are we day drinking?" Tilly asked, propping herself up on her elbows.

"I am," Mike said. "Want one?"

"Absolutely."

He handed her a beer, and when their fingers touched, he felt—something. A spark, a charge, something that made him hold the contact for just a fraction longer than necessary.

Tilly's eyes met his, and for a moment, there was something there. Something that wasn't quite casual, wasn't quite innocent.

Then she smiled and took the beer, and the moment passed.

"You're a bad influence," she said, taking a sip.

"I try."

Sarah and Mia were deep in conversation about their mother, something about a birthday party, and Mike settled onto his towel, trying to relax into the sun and surf and the simple pleasure of a day at the beach.

But he was acutely, impossibly aware of Tilly three feet away from him.

She was lying on her stomach now, bikini top untied to avoid tan lines, and Mike could see the curve of her back, the dimples above her ass, the length of her legs.

"Mike, can you get my back?" Tilly asked, holding up a bottle of sunscreen without looking at him.

Mike's brain short-circuited. "Uh—"

"Sure," he said, after thinking for far too long and distractedly taking the bottle.

He squeezed sunscreen into his palm and tried to approach this clinically, practically. It was just sunscreen. Just skin. Nothing weird about it.

Except it was weird, because the moment his hands made contact with Tilly's back, he felt that charge again—stronger this time, unmistakable.

Her skin was impossibly soft, warm from the sun. Mike spread the sunscreen across her shoulders, trying to be quick, efficient, professional.

"You can go lower," Tilly said, her voice muffled against her towel. "I burn easily."

Mike's hands moved down her back, and he was suddenly aware of every point of contact—his palms against her spine, his fingers spreading across her ribs, the way she shifted slightly under his touch.

"That's good," she said finally. "Thanks."

Mike pulled his hands back like he'd been burned and wiped them on his towel. Sarah had already returned to her conversation with Mia, completely oblivious.

But when Mike glanced at Tilly, she was looking at him over her shoulder, and the expression on her face was knowing.

She knew exactly what she was doing.

Mike grabbed his beer and took a long drink, trying to ignore the fact that his hands were shaking slightly.

This was going to be a very long day.

After twenty minutes of trying and failing to relax, Mike stood up. "I'm going to hit the water. Anyone want to come?"

"Yes!" Mia jumped up immediately. "Sarah, come on."

Sarah looked up from her book. "You two go. I'm just getting comfortable."

"Tilly?" Mia asked.

"I'm good for now. I'll watch your stuff."

So Mike and Mia headed to the water, leaving Sarah reading and Tilly sunbathing. The ocean was cold enough to be shocking, and Mia shrieked when a wave hit her.

"It's freezing!"

"You get used to it," Mike said, diving under.

They played in the waves for a while, Mia talking about her summer plans, her classes in the fall, a guy she'd been seeing casually. Mike listened and offered appropriately big-brotherly advice, grateful for the distraction, for the cold water, for anything that wasn't thinking about Tilly's skin under his hands.

When they finally headed back, Sarah had joined Tilly on the towels, and they were deep in conversation. Mike grabbed his towel and dried off, trying not to look at Tilly, trying not to notice that she'd retied her bikini top and was now sitting up, arms wrapped around her knees in a way that somehow made her look both innocent and incredibly sexy.

"I'm going to grab some food," Mia announced. "Anyone want anything?"

"I'll come with you," Sarah said, standing up. "Mike? Tilly?"

"I'm good," Mike said.

"Same," Tilly added.

And then Sarah and Mia were walking toward the concession stands, and Mike was alone with Tilly.

For a moment, neither of them spoke. Then Tilly turned to look at him, and her smile was slow and deliberate.

"So," she said. "That was interesting."

"What was?"

"The sunscreen." She tilted her head. "Your hands were shaking."

Mike's heart kicked against his ribs. "I don't know what you're talking about."

"No?" Tilly shifted closer, and suddenly she was right next to him, close enough that he could smell her sunscreen and perfume. "Because I think you do."

"Tilly—"

"It's okay," she said softly. "I felt it too."

Mike should shut this down. Should make a joke, change the subject, do literally anything except sit here with his wife's sister's best friend admitting that there was something between them.

Instead he heard himself say, "This is a bad idea."

"Probably," Tilly agreed. Her hand moved to his thigh, just resting there, casual enough that anyone looking from a distance wouldn't think twice. "But you're thinking about it anyway."

"I'm married."

"I know." Her hand moved slightly higher. "I'm not asking you to leave her. I'm just saying... there's something here. And we both feel it."

Mike looked toward the concession stands. He could see Sarah and Mia in line, talking, completely unaware.

"They'll be back soon," he said.

"I know." Tilly's hand moved again, and now it was high enough on his thigh that there was no pretending it was casual. "So tell me—if we had more time, if they weren't coming back, what would you do?"

Mike's brain was screaming at him to stop this, to move her hand, to establish boundaries.

But his body had other ideas.

"I'd kiss you," he said, voice rough.

Tilly's smile widened. "What else?"

"I'd put my hands on you. I'd—" He stopped, some last shred of sanity reasserting itself.

"You'd what?" Tilly's hand was moving in small circles now, getting closer to where he was rapidly getting hard.

"Tilly, we can't—"

"I know." She pulled her hand back, and Mike felt the loss of contact like a physical ache. "But it's fun to think about, isn't it?"

She stood up, stretching in a way that thrust her chest forward, and Mike had to look away before he did something stupid.

"I'm going to cool off in the water," she said. "You should probably do the same."

Then she walked toward the ocean, and Mike watched her go, his heart pounding, his swim trunks uncomfortably tight.

When Sarah and Mia returned with food, Mike was in the water, letting the cold work its magic, trying to get his body under control.

This was insane. This was dangerous. This was—

Tilly dove under a wave and came up laughing, her hair slicked back, water running down her body. She caught Mike looking and smiled.

This was trouble.

And Mike was starting to think he wanted it anyway.

The afternoon stretched out in a haze of sun and salt and tension so thick Mike could barely breathe through it.

Sarah and Mia had settled into comfortable sister rhythm—trading gossip, laughing at inside jokes, occasionally roping Mike into conversations that he navigated on autopilot. He gave the right responses, laughed at the right moments, played the role of attentive husband and brother-in-law.

But his attention was elsewhere.

Tilly had come back from the water and stretched out on her towel, droplets still clinging to her skin, and Mike had watched them slide down her stomach with an intensity that bordered on obsessive. She'd caught him looking—of course she had—and the small smile that curved her lips was pure satisfaction.

She knew exactly what she was doing to him.

Around two o'clock, Mia suggested they play frisbee. Sarah begged off, claiming she was too comfortable to move, and Tilly joined in with enthusiasm. Mike found himself running in the sand, diving for catches, acutely aware every time Tilly's body moved—the bounce of her breasts in that white bikini top, the flex of her thighs, the way she bent to pick up the frisbee.

At one point she threw it deliberately short, and when Mike jogged over to get it, she was right there, close enough to touch.

"You're good at this," she said, slightly breathless.

"Used to play in college."

"I bet you were good at a lot of things in college." Her eyes traveled down his body slowly, appreciatively. "Still are."

Mia called for the frisbee, and the moment broke. But Mike's heart was racing, and it had nothing to do with the exercise.

When they finally collapsed back on the towels, Sarah announced she was going to take a walk down the beach to look for shells. "Anyone want to come?"

"I'll go," Mia said immediately. "I need to move or I'm going to fall asleep."

"Mike? Tilly?"

"I'm beat," Mike said, which wasn't entirely a lie. "I'll hold down the fort."

"Same," Tilly added. "Too much sun. I need to just lie here and recover."

Sarah leaned down and kissed Mike's forehead. "We won't be long. Maybe twenty minutes?"

"Take your time," Mike said, and meant it in ways Sarah couldn't possibly understand.

He watched them walk away—Sarah and Mia side by side, heads bent together in conversation, getting smaller as they moved down the beach. When they were far enough away that he could barely make out their features, Tilly spoke.

"Finally."

Mike turned to look at her. She was lying on her side, propped up on one elbow, watching him with an expression that was pure hunger.

"Tilly—"

"Twenty minutes," she said softly. "That's what Sarah said. Twenty minutes where they're not here, where no one's paying attention to us."

"There are people everywhere." Mike gestured at the beach around them—families, couples, clusters of teenagers.

"No one's looking at us." Tilly's hand moved to his arm, fingers tracing patterns on his skin. "No one cares about two people lying on towels talking."

"We shouldn't—"

"You keep saying that." Her hand moved higher, to his shoulder. "But you don't mean it. If you meant it, you would have moved away from me by now. You would have gone with Sarah and Mia. You would have done literally anything except stay here alone with me."

She was right. Mike knew she was right.

"Tell me what you're thinking," Tilly said, her voice dropping lower. "Right now. What's going through your head?"

Mike's brain was a chaotic mess of desire and guilt and rationalization. But what came out was honest: "I'm thinking about how much I want to touch you."

Tilly's eyes darkened. "Where?"

"Everywhere." Mike's hand moved of its own accord, finding her hip. The skin there was warm and soft and forbidden. "I want to put my hands all over you. I want to find out what sounds you make. I want—"

He stopped, but Tilly was already moving closer, and suddenly there was no space between them at all.

"What else?" she whispered. "Tell me what else you want."

"I want to kiss you." Mike's hand slid from her hip to the small of her back. "I want to taste you. I want to make you come."

Tilly made a small sound—half gasp, half moan. "Fuck, Mike."

“That too" he said, the words spilling out now, uncensored. "I want to know what you feel like. I want to hear you say my name when you come."

"Yes," Tilly breathed. "Yes to all of that."

They were so close now that Mike could count her eyelashes, could see the flecks of darker blue in her eyes, could feel her breath against his lips.

"We can't do this here," he said, even as his hand tightened on her back.

"I know." Tilly's hand slid down his chest, over his stomach, stopping just above the waistband of his swim trunks. "But we could go somewhere."

"Where?"

"The bathhouses." Her fingers traced the waistband, not quite touching him but close enough to make him ache. "The changing cubicles. Like you said—no one pays attention. No one cares."

Mike's logical brain was throwing up every objection it could muster. They'd be caught. Someone would see. Sarah would know. This was insane.

But his body was already responding to the suggestion, already imagining what it would feel like to have Tilly in a locked room, to have permission to touch her, to take what they both clearly wanted.

"They'll notice if we're both gone," he said weakly.

“We'll be quick. In and out before they even get back."

"Tilly—"

"Tell me you don't want this." Her hand moved lower, and Mike had to close his eyes against the sensation. "Tell me you don't want to know what I taste like, what I sound like, how I feel. Tell me you're going to be able to go back to your beach house tonight and fuck your wife without thinking about me."

Mike couldn't tell her that. Because it would be a lie.

"Five minutes," Tilly said, and before Mike could respond, she was standing up, grabbing her beach bag. "I need to rinse off. All this salt water."

She walked toward the bathhouses, and Mike watched her go, his heart pounding so hard he thought it might actually crack a rib.

This was his chance to stop this. To stay on his towel, wait for Sarah and Mia to come back, pretend this conversation never happened.

He looked down the beach. Sarah and Mia were still visible, but distant—maybe a quarter mile away, bent over looking at something in the sand.

Mike looked back toward the bathhouses. Tilly had disappeared around the corner.

Five minutes, she'd said.

Mike counted to sixty. Then did it again. Then again.

On the fourth repetition, he stood up.

His legs felt strange as he walked across the sand—disconnected, like they belonged to someone else. Someone who made terrible decisions. Someone who was about to blow up his entire life for twenty minutes with a twenty-three-year-old.

The bathhouses loomed ahead, concrete and utilitarian and completely inappropriate for what he was about to do.

Mike walked past the restrooms, past the outdoor showers where a few people were rinsing off. His pulse was hammering in his ears, drowning out the normal beach sounds.

The changing cubicles were around the corner, a row of individual stalls. Most were empty. A few showed occupied.

Mike walked slowly down the row, trying to look casual, trying not to look like exactly what he was—a married man about to commit adultery with his wife's sister's best friend.

A door opened near the end of the row.

Tilly stepped out, and when she saw him, her smile was slow and knowing and absolutely certain.

She didn't say anything. Just stepped back into the cubicle, leaving the door open.

This was it. This was the moment. Mike could turn around right now, walk back to the beach, and pretend this had never happened.

Or he could step through that door.

He glanced around. A woman was coming out of the restroom with a small child. A teenage boy was at the showers. No one was looking in his direction. No one cared.

Mike stepped into the cubicle.

Tilly pulled him in further and pushed the door closed behind him. The lock clicked with a sound that seemed impossibly loud.

The space was tiny—barely big enough for one person, let alone two. There was a wooden bench along one wall and hooks for clothes. It smelled like salt water and concrete and Tilly's perfume.

They stood there for a moment, not quite touching, both breathing hard.

"Hi," Tilly said softly.

"Hi." Mike's voice came out rough.

"You came."

"Yeah."

"I wasn't sure you would." Her hand came up to rest on his chest, right over his heart. "You seemed pretty conflicted."

"I am conflicted."

"But you're here anyway." Tilly's smile was satisfied. "Why?"

"Because I can't stop thinking about you," Mike admitted. "Because I haven't been able to think about anything else since you got in my car this morning. Because—"

Tilly kissed him.

Not tentative, not testing. Full and deep and hungry, her tongue sliding into his mouth, her body pressing against his. Mike's hands found her waist automatically, and the feel of her skin under his palms—warm and soft and so fucking alive—made something break loose in his chest.

He kissed her back, pouring all the wanting from the past few hours into the slide of lips and tongue. She tasted like beer and something sweet, and she made small sounds against his mouth that were going to drive him insane.

When they broke apart, both breathing hard, Mike was already fully hard against her hip.

"Fuck," Tilly breathed. "I've been wanting to do that all day."

"Me too."

She kissed him again, harder this time, her hands in his hair, pulling him down to her. Mike's hands slid from her waist to her ass, pulling her closer, and Tilly made a sound that was pure encouragement.

"We don't have much time," she whispered against his mouth.

"I know."

"So tell me—" Her hand slid down between them, palming him through his swim trunks. "What do you want? What do you want to do to me in the next fifteen minutes?"

Mike groaned at the contact, his hips pushing into her hand involuntarily. "Everything. I want everything."

"Be specific." Tilly squeezed him through the fabric. "Tell me exactly what you've been thinking about."

"I want to taste you," Mike said, voice rough. "I want to put my mouth on you and make you come on my tongue."

"Yes," Tilly breathed. "What else?"

"I want to fuck you." His hands found the ties of her bikini bottoms. "I want to be inside you. I want to know what you feel like."

Tilly's eyes were dark with want. "We can't do everything. Not enough time. So choose—do you want to taste me, or do you want to fuck me?"

It was an impossible choice. Mike wanted both, wanted everything, wanted hours instead of minutes.

But they didn't have hours.

"Both," he said. "I want both."

Tilly laughed quietly. "Greedy. I like it." She turned to face the wall, hands braced against it, looking back at him over her shoulder. "Then you better work fast."

Mike's hands went to the ties of her bikini bottoms, and he paused for just a second—one last moment of sanity trying to break through.

"Are you sure?" he asked.

"Mike, if you don't put your hands on me in the next five seconds, I'm going to scream. And not in a good way."

He pulled the ties.

The white fabric fell away, and Mike's breath caught. She was perfect—everything young and toned and forbidden. He could see how wet she already was, could see the evidence of her arousal, and it made his cock ache.

He dropped to his knees on the concrete floor.

The floor was hard and gritty, and he knew his knees would hurt later, knew there would be marks he'd have to explain to Sarah. But none of that mattered because Tilly was right there in front of him, and when he leaned in and put his mouth on her, she tasted like salt and arousal and sin.

"Oh fuck," Tilly breathed, her hand flying to her mouth to muffle the sound.

Mike didn't tease, didn't build slowly. They didn't have time for that. His tongue worked against her in long, deliberate strokes, learning her quickly, finding what made her thighs shake.

She was already wet, getting wetter, and the taste of her was overwhelming. Mike gripped her ass with both hands, pulling her back against his face, and Tilly's knees buckled slightly.

"God, Mike," she whispered against her palm. "That's so—fuck—"

His tongue found her clit and worked it in steady circles, and Tilly's whole body started to tremble. He could feel her getting close, could feel the tension building in her muscles.

Outside the cubicle, he heard voices—two women, talking about lunch plans. The voices got closer, and Mike froze, his face still buried between Tilly's legs.

The voices passed by without stopping, and Mike started moving again, his tongue working faster now, more urgently. Tilly was making muffled sounds that were getting louder despite her hand over her mouth, and Mike knew they needed to be quieter but he couldn't stop, didn't want to stop.

He slid two fingers inside her while his tongue kept working her clit, and Tilly's hand scrabbled against the wall, looking for purchase.

"Close," she breathed. "So close, don't stop—"

Mike crooked his fingers, finding that spot inside her, and kept the pressure steady with his tongue. Tilly came with a strangled sound she barely managed to muffle, her whole body shuddering, clenching around his fingers.

He worked her through it, gentler now, drawing it out, until the aftershocks finally subsided and she sagged against the wall.

Mike stood up slowly, his knees protesting, and Tilly turned to face him. Her eyes were glazed, her lips parted, her whole body still trembling slightly.

"Holy fuck," she breathed.

"Good?" Mike asked, though he knew the answer.

"So good." She reached for him, pulling him into a kiss—deep and thorough, tasting herself on his tongue. When she pulled back, her eyes were hungry again. "Now fuck me."

"We don't have time—"

"We have enough time." Her hand went to his swim trunks, pulling them down. His cock sprang free, and Tilly's eyes widened slightly. "Jesus, Mike."

She wrapped her hand around him, stroking slowly, and Mike had to brace himself against the wall.

"Condom?" she asked.

"I don't have one."

"I'm on the pill. And I'm clean." Tilly's eyes met his. "Are you?"

"Yes."

"Then fuck me." She turned back to face the wall, bending forward slightly, one hand braced on the bench. "Right now. Before we run out of time."

Mike's hands found her hips, and he could feel her heat, could feel how wet she still was. One thrust and he'd be inside her, would be fucking someone who wasn't his wife for the first time in eight years.

He should stop. Should pull back, get dressed, walk away.

Instead he pushed forward.

The first inch made them both gasp. Tilly was tight—incredibly tight—and Mike had to pause, giving her time to adjust.

"More," Tilly breathed. "All of it."

Mike pushed in slowly, steadily, until he was buried to the hilt. The sensation was overwhelming—the heat, the tightness, the absolute wrongness of it that somehow made it more intense.

"Move," Tilly whispered. "Please, Mike, move."

He pulled back and thrust in again, and Tilly's hand flew to her mouth to muffle her moan. Mike found a rhythm—deep, steady strokes that made Tilly push back to meet him.

The sound of skin on skin seemed impossibly loud in the small space. Mike knew they needed to be quieter, knew they were taking an insane risk, but Tilly felt so good, so perfect, and he couldn't stop.

"Harder," Tilly breathed against her palm.

Mike complied, his hips snapping forward with more force, and Tilly's knees buckled slightly. He had to hold her up, one arm wrapped around her waist while he fucked her.

"You feel so good," he groaned. "So fucking good."

"Yeah?" Tilly looked back at him, and her expression was pure lust. "Better than Sarah?"

The question should have killed his arousal, should have brought guilt crashing back.

Instead it made him thrust harder.

"Don't," Mike said, but there was no conviction in his voice.

"It's okay," Tilly breathed, pushing back to meet his thrusts. "You can admit it. You can tell me how different I feel. How tight. How wet."

Mike's grip on her hips tightened, and he knew he was going to leave bruises—marks that would still be there tomorrow, evidence of what they'd done. "You're so tight," he groaned. "So perfect."

"Keep going," Tilly urged. "Don't stop. I want to feel you come inside me."

The words sent a jolt through him. He was fucking his wife's sister's best friend raw in a beach bathroom, and she wanted him to come inside her. The depravity of it should have disgusted him.

It just made him fuck her harder.

Outside the cubicle, Mike heard footsteps—close, getting closer. Multiple people, voices overlapping.

He froze mid-thrust, panic flooding his system.

The footsteps stopped. Right outside their door.

"This one's occupied," a woman's voice said—young, cheerful, completely oblivious.

"There's another one down there," her friend replied.

The footsteps moved away, and Mike's heart was hammering so hard he thought it might actually stop. That was too close. Way too fucking close.

But Tilly was already moving again, pushing back against him, and Mike's body responded before his brain could catch up.

"We should stop," he said, even as he thrust deeper.

"We should," Tilly agreed, her hand still over her mouth to muffle her sounds. "But we're not going to."

She was right. They weren't going to stop. Mike could feel his orgasm building, could feel it coiling at the base of his spine. Tilly seemed to sense it because she started moving with more urgency, matching his rhythm.

"I'm close," Mike warned. "Tilly, I'm—"

"Do it," she breathed. "Come inside me. I want it."

Mike's rhythm faltered, became erratic. He thrust deep three more times and came with a groan he barely managed to muffle against Tilly's shoulder. The orgasm ripped through him with an intensity that made his vision white out at the edges, and he felt Tilly clench around him, felt her own orgasm triggered by his.

They stayed like that for a long moment, both breathing hard, Mike's forehead resting against her back. He could feel his heart hammering, could feel the sweat cooling on his skin, could feel the full weight of what they'd just done settling over him like a blanket.

He'd just fucked Tilly. Had just come inside her. While Sarah—his wife, the woman he'd promised to be faithful to—was walking on the beach with her sister, completely trusting him, completely unaware.

The guilt should have been crushing.

But all he felt was satisfied in a way he hadn't felt in years, and already thinking about when they could do this again.

Tilly straightened slowly, and Mike slipped out of her. She turned to face him, and they looked at each other in the dim light of the cubicle. Her hair was messed up, her lips swollen, her eyes still dark with residual arousal.

"Hi," she said softly.

"Hi," Mike replied.

She laughed quietly and kissed him—gentle this time, almost tender. When she pulled back, she was smiling.

"That was..." she trailed off.

"Yeah," Mike agreed.

They started getting dressed, awkward in the small space, bumping into each other. Tilly tied her bikini back on, finger-combed her hair. Mike pulled his swim trunks up and tried to make himself look like someone who hadn't just committed adultery in a beach bathroom.

"I should go first," Tilly said, checking her reflection in the small mirror mounted on the wall. "You wait a few minutes, then come back separately."

"Okay."

She paused with her hand on the lock, looking back at him. "No regrets?"

Mike thought about Sarah. About the life they'd built together, the promises they'd made. About how easily he'd just broken those promises.

"No regrets," he said, and wasn't entirely sure if it was a lie.

Tilly smiled, unlocked the door, checked that the coast was clear, and slipped out.

Mike stood alone in the cubicle, listening to her footsteps fade away. He could smell her perfume, could smell sex, could smell his own guilt and satisfaction mixing into something complicated he didn't want to examine too closely.

He waited five minutes that felt like hours, then stepped out of the cubicle. The corridor was empty. He walked to the outdoor showers and rinsed off, washing away the evidence, trying to wash away the expression he knew was on his face.

Then he walked back down to the beach.

Sarah and Mia were back at their spot, and when Sarah saw him, she waved. "There you are! We found the most amazing shells. Where'd you go?"

"Just rinsed off," Mike said, settling onto his towel. "All the salt was getting to me."

Tilly was already back on her towel, and when he glanced at her, she was looking at her phone, completely casual, like nothing had happened.

"Did you see Tilly while you were up there?" Mia asked. "She went to rinse off too."

"Nope," Mike said easily. "Must have just missed each other."

Sarah launched into a story about the shells they'd found, and Mike nodded along, giving appropriate responses, playing the role of attentive husband.

But under his towel, his phone buzzed.

He pulled it out casually, glancing at the screen.

A text from an unknown number: That was incredible. When can we do it again?

Mike's heart kicked against his ribs. He glanced at Tilly, who was still looking at her phone, a small smile playing at her lips.

He should delete the text. Should shut this down right now before it went any further.

Instead he saved her number and typed back: Soon.

Her smile widened, and she looked up at him through her lashes, and Mike knew with absolute certainty that this was just the beginning.

The rest of the afternoon passed in a haze of normalcy that felt surreal. They swam, they ate sandwiches from the cooler, they played cards in the shade of the umbrella. Sarah was relaxed and happy, Mia was entertaining, and Tilly was the perfect friend—funny, charming, completely appropriate.

No one would have guessed that less than an hour ago, Mike had been inside her.

But every time their eyes met, Mike felt that charge again. Every casual touch—passing sunscreen, reaching for the same bag of chips—carried weight that no one else could see.

Around four o'clock, Sarah suggested they start packing up. "We should get back, get cleaned up before dinner."

They loaded everything into the car, and Mike found himself in the back seat this time, Tilly next to him, their thighs pressed together in the confined space.

Sarah and Mia were in front, talking about dinner plans, debating between the seafood place and the Italian restaurant. Mike contributed to the conversation when required, but his attention was on the point where his leg touched Tilly's, on the heat radiating between them.

Tilly's hand moved to his thigh—casual, like she was just getting comfortable. But her fingers traced small circles against his skin, and Mike had to focus on breathing normally.

"What do you think, Mike?" Sarah asked, glancing back at him in the rearview mirror.

"Hmm?"

"Seafood or Italian?"

"Either's good with me."

Sarah laughed. "You're so helpful."

Tilly's hand moved higher, and Mike had to cough to cover the sound he almost made.

When they pulled up to the beach house, Mia and Tilly gathered their things. "Thanks so much for today," Mia said, hugging Sarah. "This was exactly what we needed."

"Anytime," Sarah said warmly. "We should do it again before the summer's over."

"Definitely," Tilly agreed, and when she hugged Mike goodbye, she pressed against him just slightly longer than necessary, and whispered in his ear: "Check your phone later."

Then they were gone, walking down the street toward their summer rental, and Mike was alone with Sarah.

"That was fun," Sarah said, unlocking the front door. "I'm so glad we did that."

"Me too," Mike said, and meant it in ways Sarah couldn't possibly understand.

They showered—separately, Sarah going first while Mike checked his phone.

Another text from Tilly: I can still feel you inside me.

Mike's cock twitched, and he typed back: Good.

When can I see you again?

I don't know. This is complicated.

I know. But you want to.

Mike stared at the message, his thumb hovering over the keyboard. He should say no. Should end this now before it went any further, before someone got hurt.

But he thought about the way Tilly had felt, the sounds she'd made, the way she'd looked at him like he was the only thing that mattered.

Yes, he typed. I want to.

Then we'll figure it out. I'm patient.

Mike deleted the conversation and put his phone away just as Sarah came out of the bathroom, wrapped in a towel.

"Shower's all yours," she said, kissing his cheek.

Mike showered, washing away the salt and sand and evidence, watching it all swirl down the drain. When he came out, Sarah was getting dressed for dinner, and she smiled at him in the mirror.

"You got some sun today," she said. "You look good."

"Thanks."

She turned to face him, and her expression was soft, affectionate. "I love you, you know that?"

Mike's chest tightened with guilt that he pushed down, buried deep. "I love you too."

And he did. He really did.

But as they got ready for dinner, as Sarah talked about her day and laughed at something Mia had said, Mike's phone buzzed again.

He didn't check it. Didn't need to.

He already knew it was Tilly.

And he already knew that no matter how much he loved Sarah, no matter how wrong this was, he was going to see Tilly again.

The question wasn't if.

It was when.