AN ~ Setting etc. explains itself. Spoilers for season six. As you can guess by now, inspired by that particular quote from The Doctor, the Widow and the Wardrobe. I thought it was so touching, I just had to write something...but this is not another what-happens-after-he-goes-through-the-door-for-Christmas.
The Doctor's feet were heavy as he stepped onto Amy and Rory's minuscule threshold-turned-porch. He stared at his black boots, still speckled and smudged with the metallic purple mud of Darillium, until a cheerfully laughing Amy swung the door open, spilling light on the hunched figure on the doorstep which seemed, to him, false and useless.
He looked up, and as if he was seeing her through a glass window, studied Amy Pond's expression without a word. She was frozen, shocked and concerned, water pistol raised for old time's sake but the other hand clinging to the door frame as if his posture somehow warned her that the world was caving in.
"Rory!" she called. "Roraaay!"
The Roman came running, and behind him, a puzzled, frizzy-haired blonde in riding attire, Vortex Manipulator flashing from her wrist. Her expression almost immediately changed when the message reached her brain.
"Hello, Sweetie," she greeted him with a broad grin; this was definitely a surprise of the pleasant kind. Her greeting seemed to reset something in the Doctor, as if she had flicked a switch. He straightened, and smiled, and took the water pistol from Amy.
"Icecream on Star 56!" he announced, squirting the three faces opposite him to rid them of their stunned expressions, and then tucking the plastic pistol into the deep recesses of one of his jacket pockets. The three of them fumbled, pushed and pulled, and after a few seconds made it onto the front lawn. River, though she could tell something was wrong with the Doctor, hurried her parents towards the Tardis. Rory uncertainly played along, but Amy stayed put.
"What's going on?" Amy demanded. "Doctor? What's wrong?"
She locked her eyes on his, and saw the glistening facade give way again. But the Doctor was still wearily smiling.
"I'm thirteen hundred years old. There's a lot wrong, Pond. But tonight I don't want to think about it. I want icecream. Is that okay?"
And he guessed it was, because she threw his arms around him in such a way that pinned his arms to his side, so that he could not hug her back. It was an embrace of forgiveness and comfort and promises. Oh, Amelia. So much faith in him.
He watched her spring towards the Tardis, and followed with an unusually sombre gait. With some effort, he sprung over the threshold. It made him feel a little better, to his pleasant surprise, but it did not quash the guilt that burned him up from the inside – like flames blackening and curling paper, only slower. He could certainly not tell Amy and Rory about the Library in River's presence, or anywhere near her presence, but he would have to tell them soon. He would have to keep coming back, keep facing them, until he found the right moment.
But really, he thought to himself, is there ever a right moment for such news?
Suddenly, he was knocked out of his woefulness by River Song, pulling him into a lively Jitterbug-style dance in time to a cheerful tune. He staggered and stumbled as she tried to direct him, and he realised that this incarnation was possibly the worst he'd ever had at dancing. And that was saying something.
"So, Star 56?" River queried. He had the feeling she was checking the information more than anything else, but he may have misinterpreted her tone: he was busy focusing on a fiery tango-style, one-armed dip. This dancing stuff was fun. (Though, unbeknownst to him, River was holding herself up with one arm on the Tardis console, already starting to direct them towards the best icecream this side of the Medusa Cascade.)
"Oi, watch your hands," Amy growled a warning.
The Doctor pulled River back to her feet, and as the cheerful music continued she danced over to her mother, the two of them looking completely stupid but clearly enjoying it. Rory, however, was watching the Doctor with one eye. He sidled over.
"I'm not going to talk about it," the Doctor informed him before he could get a word out. "The time isn't...right."
"For us, or for you?" Rory countered.
"It's bad news, Rory, you know that. Bad news and icecream should never go together."
"But fish fingers and custard..?"
The Doctor snorted with laughter. "That's more like it."
The Tardis whirred as she materialised, and the Doctor opened the doors for his companions with an honest – if not 100% enthusiastic – smile. With a cheerful tune in the background and his still stupidly dancing friends ahead of him, his hearts lifted, and he wondered with a sting of guilt how this could be. It should be killing him inside, seeing them so happy like this, when he knew that he would have to take it all away.
"Because every time you see them happy you remember how sad they're going to be, and it breaks your heart. Because what's the point in them being happy now if they're going to be sad later?"
He put his hand over his pocket, now empty of its sonic screwdriver. Ten minutes ago, that had been as gaping a hole as the crack in time. Now it did not feel nearly so galactic. In fact, he recalled that in that very same pocket was the receipt from chips with Rose Tyler, a little soap from Midnight with Donna, and an ear that had once broken off K-9.
"Hey!" Amy called from somewhere out of sight. "This icecream ain't gonna buy itself!"
The Doctor's eyes glistened.
"The answer is, of course, because they are going to be sad later."
He pulled a stick of credits from another pocket, and ran to find his friends.