When Spock entered his quarters, he wasn't particularly surprised to see Doctor McCoy there, sitting in one of the chairs. He nodded at him and made his way towards the sleeping area to change after his shift.

"I was thinkin', we might play."

Spock stopped and looked back at McCoy. He was still in his own uniform - the only concession to his off-duty status was the lack of boots on his feet. Spock looked him over, tilting his head.

"When you say, play…"

McCoy gestured at the 3D Chess set on the table. "I've been… practising."

Spock's lips twitched, and he made his way over, all thoughts of changing forgotten.

"You believe that you can beat me?"

McCoy smirked. "Probably not."

Spock's eyes narrowed as he sat down across from him. "Then what would be the purpose of playing?"

McCoy shrugged. "Perhaps we could make it more interesting, then?"

Spock swallowed. "Interesting how?"

McCoy just smiled. "Play me and find out."

Spock picked up a white pawn and moved it forward two spaces.

McCoy looked at the board, studying it for a few moments, then made his move.

They continued for several minutes, until Spock captured one of McCoy's pawns.

"Knew I shouldn't've moved that one." McCoy licked his lips, looked up at Spock, and grinned. Spock stared at him, confused. McCoy stood up, stretched, and pulled off his uniform tunic in one quick movement. He folded it up and placed it gently on the back of his chair then sat back down.

Spock licked his lips, and waited.

Several moves later, Spock captured another piece - a rook this time. McCoy swore under his breath, and stood again. This time, the black undershirt joined his blue tunic, and he sat back down.

Spock swallowed against the sudden warmth in his skin.

"Doctor, I-"

McCoy moved, and captured one of Spock's knights. He looked up into Spock's eyes, then down at his tunic. "Your turn."

Spock let out a breath, then carefully pulled his tunic off. When he looked back up, McCoy's eyes were bright with amusement.

It took only two more moves, and Spock captured another pawn. McCoy pulled off one sock. McCoy captured two pawns in a row, and Spock removed his own socks, stubbornly keeping the undershirt on for the moment.

Another pawn of McCoy's left the board, and the other sock came off. Spock found himself mesmerised by the way McCoy would curl his toes as he thought about his next move, or the way his fingertips would unconsciously rub at his collarbone, or…

Spock shook his head, and looked back at the board.

When he captured one of McCoy's bishops, he held it for a moment, looking across the board. McCoy held his gaze as he stood up and very slowly, very deliberately, unbuttoned his trousers.

Spock forced himself to keep his eyes on McCoy's face, tracking it as he leaned over. In his peripheral vision he could see McCoy's thumbs tucked into the waistband - a waistband which was sliding down, over his thighs.

Spock held his breath.

McCoy sat down, pulling his trousers off his feet. He stood again and folded them. His eyes were still on Spock's face.

Spock stared up at him.

"You look a bit green, Commander."

Spock blinked quickly and looked at the board. "It was… a long shift."

McCoy sat down, legs splayed out in what Spock was certain was an entirely indecent fashion. The black regulation briefs stood out distinctly against McCoy's light skin, and Spock couldn't stop himself from glancing at it each time McCoy shifted in his seat.

McCoy took a rook, and Spock lost his undershirt. The next move, McCoy captured Spock's second knight. Spock hesitated.

"Something wrong, Commander?"

Spock sucked in a breath, shook his head, and stood up. He began to unfasten his trousers, then looked up, watching McCoy's reaction.

McCoy's eyes rolled slowly up his body until they met his own. Then Spock pushed his trousers over his hips.

When he stepped out of them, he glanced down at the floor.

"I confess that I…" He took a calming breath. "I had not considered how… interesting… chess might be, with such an element added to it."

McCoy chuckled. "Wait 'til you see what I'm thinking about for whoever loses these first." He snapped the waistband of his briefs.

Until then, Spock had never lost a piece so purposely quick in his life.

But it was worth it.