The Doctor never realised how lucky he was until now, living through people's lives more or less in order. Not always, of course, there were the odd acquaintances he caught out of order - Shakespeare, for one - but that was different. Shakespeare didn't make a habit of grabbing him and snogging him, for instance.

River let him go after a moment. The Doctor didn't move, just stared at her open-mouthed, searching for words. She studied his face for a moment, and then just laughed. "Oh, you're young. In that case, I'd apologise for the kissing, but I wouldn't mean it."

"River!" he finally said, squeaking a little. "You're-"

He wasn't sure what he meant to say. Alive. Here. Real. All of those seemed like very bad things to say. His lips were tingling from the kiss, and he couldn't decide if he wanted more to hug her or run away.

River, in the end, made the decision for him by apparently deciding he wasn't going to finish the sentence and asking, "Since you're here, do you happen to know anything about psychovores?"

It seemed strange to have someone else on the TARDIS after Donna. He didn't want anyone there, certainly didn't need them, not when it always ended the same way, every time. River either didn't notice, or didn't care, because after they'd sorted the psychovores, after it seemed they'd go their separate ways, River took one look at his face, tilted her head to the side, and said calmly, "I've been thinking about taking a trip."

She didn't have a room in the TARDIS. Not yet. She grumbled good-naturedly about none of her things being there, books and clothes and all, and yet calmly selected a room that hadn't been used for years and settled in there, telling him they could go when she'd slept, and the destination was his to choose.

He wandered away for a few hours, poking absently at the controls, considered sleeping and decided - as he had for the past... he couldn't remember how long - that he wasn't actually that tired. He came back later, nudged open the door she hadn't closed entirely and stood there in the doorway, watching her sleep in the half-light.

People he had travelling with him... it ended the same way every time, but this time he could see it coming. This time he'd already lost her. He wasn't certain that helped.

Another thing he never realised was how lucky he had been that when he travelled with Jack, he'd mostly been able to cow him into behaving. With River, the combination of 51st century shamelessness and being totally unimpressed by the Doctor...

The Doctor walked into the room, paused just long enough to register River, curled up and scribbling in her diary, and much more bare skin than he'd really bargained on seeing, and recoiled, one hand clapped over his eyes. "River! Could you... ah... put on a shirt? Please?"

She put her diary down, and looked up. At least, he assumed she did, being as he couldn't actually see her. He heard what sounded like a book being set softly on a table, and a slight shifting of position. "It was hot," she answered simply. The Doctor peeked through his fingers, just for a second and... no. No, she was not putting on a shirt.

"You couldn't just... turn on the air?"

"I would, but you've never actually taught me how to work the air conditioning in the TARDIS."

"Ah. Well. Um."

He heard a shift that sounded like she might be standing up. He decided not to drop his hand just yet.

"Doctor. They're breasts. You've seen them before. You've touched them before."

"Not yet I haven't!"

That day, the Doctor taught River Song how to set the temperature on the TARDIS, not that doing so really helped anything at all.

He knew when River was ready to leave the TARDIS. She didn't have to say anything, she just looked at him, and he recognized that look, remembered it from when Martha left... Except he'll be seeing her again. Again and again, and he'll know before it's over.

"Home again, then?"

She smiled at him, and nodded. "If you wouldn't mind. I hate to leave yo alone, but... I have things to do back there."

The Doctor leaned against the edge of the console, watching her out of the corner of his eye. "You know this is a time machine."

"Really?" she said, a smile playing about her lips. "Somehow I'd missed that, in all the temporal hopping."

He shrugged, trying for a smile, and started setting the coordinates. "Thought it was worth mentioning..."

A hand settled on his shoulder, River standing close enough to him that he could feel her breath against the side of his neck. "If I find out you sat here moping after I leave, I'm going to hurt you next time."

He glanced back at her, smile still set on his face. "Is that an order?"

"It may be," she said with a grin. "Go somewhere you'll enjoy - how long's it been since you had a Christmas?"

The Doctor wondered if she'd ever actually been to one of his Christmases, wondered if that look on her face meant she knew something he didn't, wondered if he should ask at all, and if the answer would simply be "spoilers". There were secrets they both had to keep, right from the start, and so instead of asking, he flipped a lever, hit a few buttons, and took her home. When River stepped off the TARDIS, she left it feeling just a little less empty than it had been before.