Originally posted on the mass effect kink meme for a "skinny dipping" prompt (Part XVI p. 27), slightly edited to bring it down to an M rating.

"I'll do it if you do it," Kaidan said, his words thick with alcohol, but only people who really knew him would be able to tell. He and Shepard were walking through the moonlit presidium on their way back to the Normandy from a night of debauchery at Purgatory.

"If I do it, you have to do it naked," Shepard countered.

"Fine. I bet you won't do it though."

Shepard raised an eyebrow and then in one quick, fluid motion pulled her tank top over her head. In another moment she'd kicked off her boots, and before Kaidan could react she was standing in front of him in her lacy black panties and bra.

"Shepard!" Kaidan hissed, suddenly panicking. "No!"

She flashed him one last wicked smile and then she was over the rail and in the water.

"SHIT it's cold!" Shepard shouted, louder than she meant to. It was also just over her head. She ducked under water and pulled off her panties and bra, then flung them up onto the walkway at Kaidan. He stared at them at his feet for a moment, and then he realized what he was looking at.

"Shepard!"

"We had a deal Alenko, so get naked!"

"Fuck no! We'll get arrested!"

"No one can arrest a Spectre, Kaidan," Shepard said. "Where's your sense of adventure? Or your balls for that matter."

Kaidan shook his head, but he wasn't about to be outdone by Shepard or go back on his word. Drunk or not, a deal was a deal. He kicked off his boots and stripped out of his shirt and pants, glancing around to make sure no one was coming-luckily the presidium was deserted at this time of night.

Shepard shivered when she caught sight of his profile in the dim light above her-his broad chest and shoulders, flat washboard stomach, and the jut of his pelvic bone above his underwear.

He jumped in, creating a splash that soaked Shepard and probably woke up everyone in a five mile radius. Shepard burst into drunken laughter and ducked under the water in front of him. Her hands found the elastic band of his underwear and she yanked them down, rendering him as nude as she was. She let them float away and then resurfaced.

"Oh shit it's cold!" Kaidan said. "You're insane Shepard!" He was a little bit taller than her and could stand up in the water, so Shepard put her hands on his shoulders to help her keep her head up.

"No, I'm not. If I was insane, I would try something like...this." She pulled herself towards him and pressed her breasts to his chest, the cold nipples rubbing against the dark wiry hairs scattered across Kaidan's pecs.

"Or this," She leaned in and kissed him, her warm breath from her cold lips was exhilarating. Kaidan responded without thinking, parting his own lips to taste her tongue. It was sweet like the rum she'd been drinking all evening, but the kiss itself was the opposite. Shepard's lips tore at his urgently, telling Kaidan just how horny she was. He moaned softly and gripped her ass under the water, pulling her against him until the beginning of his erection was growing between them.

"We can't…have sex…in the presidium lake…" Kaidan managed to gasp, but it seemed like he was wrong about that. His hard-on was full blown and Shepard's legs were locked around his waist. She kissed him harder in defiance of his protesting and before he knew it his member was slipping inside of her.

Shepard squeezed him and rocked her hips, pulling and pushing against him in the water. They were starting to cause a little splashing, which made Kaidan nervous, but there was nothing he could do to stop it. If he didn't fuck Shepard senseless right there, right then, he was going to explode. His hands clenched around her ass cheeks and he helped her along. Shepard never stopped kissing him, never stopped rubbing the hard nubs of her nipples across his chest, never stopped rocking her hips. Shepard to whimpered and moaned against him with each deep thrust. The splashing was more violent now, but Kaidan' didn't care at all.

"Oh Fuck, Oh Fuck, Oh Fuck," Kaidan closed his eyes and pulled Shepard onto him hard, shivering from cold and orgasm and how fucking insane it was that they were really doing this—had really done this. Shepard's breath quickened and her muscles spasmed as she climaxed, sending aftershock orgasms through Kaidan's whole body. He buried his face in her neck and just breathed, over and over, trying to get his still-drunken thoughts in order and body under control.

"That wasn't part of the bet," Shepard said. She pulled off of him and swam a little ways away. Kaidan, meanwhile, was looking for a way back up. He launched himself into the air and grabbed the bottom of the walkway that they had jumped from, then pulled himself up onto it.

"Get out of there, Shepard!" he hissed, sorting through the pile of clothes for his. "And where the fuck are my underwear?" He held up Shepard's lacy panties in front of his face. When lowered them, he found himself face to face with Captain Bailey.

"Forget your underwear, put your damn clothes on! You have two minutes to get out of here before my whole squad descends and arrests your ass for public indecency!"

Kaidan gaped. "What about her?" Shepard was still swimming about, bare-ass naked in the lake below them.

"She's a Spectre, she can do whatever the fuck she wants."

Kaidan had already pulled on his pants and gathered the bundle of clothes into his arms by the time Bailey finished his sentence. "Sorry Captain Bailey, this won't happen again!" He darted across the walkway and then broke into a run to get back to the Normandy before C-Sec could catch up to Bailey, who split in the opposite direction to intercept his men and give Kaidan a head start.

"Kaidan?" Shepard called out into the dark, empty presidium. "Kaidan!"

Epilogue:

Twenty minutes later a sopping wet, completely naked Shepard strolled onto the Normandy as if she were in her dress blues, much to the chagrin of the few people who were on deck so late. "Carry on," she said, waving away their salutes. "Nothing to see here."