A few months after the Doctor lost Amy, there came a little knock on the door. The Doctor looked up and frowned. He was not at all in the mood for society. He was sprawled on the floor of the TARDIS with a book in his hands and a mug of tea at his elbow, and as far as he was concerned, he could stay that way for the next ten thousand years.

"Hello," he muttered at the TARDIS. "Just send them off, will you? I'm busy."

The TARDIS yawped.

"Don't be like that, dear," He licked his lips and turned the page. "And I am busy. I'm… I'm…" He closed the book to look at the cover. The Lonely Robot by Amelia Williams. And he was holding it upside-down. "Coping. Grade A, number one, professional coping. Stop complaining. I'm making progress."

The TARDIS yawped again, a bit skeptically.

And there was another knock at the door, somewhat sharper this time.

"Fine," said the Doctor. "Very well." He got up and put his reading glasses in his pocket. "It's just to show that I can, though. They're not staying, whoever they are. I've had enough with houseguests. Who needs them? All they do is clutter up the place with their domestic and their bloody… mums. All we need are each other and the open sky. That's what I've always said. Haven't I always said that?" He rolled his eyes. "Don't answer that. I don't want to talk about it. I really don't."

He stalked over to the door and threw it open. Then he had to lower his gaze by two and a half feet. A boy stood on his doorstep. A smallish, skinny lad of about seven. He had a red paper crown on his head. His expression was soft and earnest. A child who'd had an easy life, then. Never missed a meal. Doted on by loving parents, et cetera. Behind the boy, the Doctor could see a sliver of pale blue sky and damp, tan sand. That meant Earth. About 2014. No. Hold on. 2013. Or the mid-teens anyway. Which was pretty interesting, because the Doctor had last parked the TARDIS in the middle of a quiet nebula in the Third Great and Bountiful Human Empire, and that was a solid billion years off. Must've forgotten to set the handbrake.

He had been a little distracted lately, what with Amy going away and all the… coping. How embarrassing. He hadn't made an error like that since driving school.

"Hullo," said the boy.

The Doctor zoned back in. "Hullo."

"I'm Simon Smith." The boy extended a small hand.

He was very formal, so the Doctor had to respond in kind. They shook. "Nice to meet you. I'm the Doctor."

Simon cocked his head. "That's a funny coincidence."

"Is it?"

"My dad's a doctor."

"Right," said the Doctor. "Good."

"Look, I'm sorry to bother you," said Simon, crossing his arms, "but where did this box come from? Only we take this walk all the time and there's never been a box here before." He peeked around the Doctor. "It's nice."

"It's not nice," said the Doctor, too quickly.

Simon looked at his shoes. "I'm sorry."

"No." The Doctor grimaced. "I'm sorry. I've not been myself lately. Yes, it's funny inside."

"Bigger, I should think," said the boy. "Like mirrors face-to-face."

The Doctor smiled. "That's clever. Did you work that out yourself?" The Doctor evaluated Simon's hat. "Is it Christmas?"

"Christmas Eve, silly," said Simon. "May I come in?"

The Doctor leaned against the doorjamb. The kid was brave. Out for a walk on Christmas Eve, weird blue box, he just comes and knocks on the door. Bold lad. The Doctor liked him. More to the point, though: Simon had seen through the perception filter. Right through it, like it wasn't there. Which probably meant a loose wire in the perception condenser. Then again, it might mean something else.

The Doctor scratched his chin. "You'd better ask your mum."

"I'm not out with my mum."

"Your dad, then."

Simon grinned, showing off an impressive set of white teeth. "All right!" He dashed off, yelling dad, dad.

The Doctor was about to slam the door and zip off. He was thinking about visiting the Tin Vagrant. He could do with some spiritual counseling, and the Balance Gardens were a good place to be alone and have a lie-in. He started to dial in the coordinates. But something told him to go easy on the controls. This wasn't just loose wiring. And there was something else too. A flavor in the air. Like… it tasted like 2013, for sure, with its special tang of Twitter, wifi and climate change, but there was something off about it.

Weird.

He huddled inside the TARDIS for a moment, then muttered, "Oh, we might as well get on with it."

He took a deep breath, marched down the walkway and stepped outside.

It was a pleasant blue day, though chilly. The wind whipped, and distant clouds promised rain later, but the Doctor never bothered very much about weather.

He shaded his eyes and looked around. The TARDIS was perched a rocky coast. The sea foamed up through the rocks with every wave. Just beyond was a long, empty beach. A bit forbidding, but the Doctor ate forbidding for lunch. With vinegar. He took a turn around the TARDIS, trailing his hand along her side. He took a deep breath of the salt air. It had been a long time since he'd been out of the box. Not since Amy. The universe had taken care of its own affairs for months and months. And we're well out of it, too, aren't we, dear, the Doctor thought, pressing his forehead against the side of the TARDIS for a moment. He was through. Utterly through. Retired. Finished. He didn't care if he spent the rest of eternity like a pearl inside its oyster.

That lad though. Sandy-haired kid. Skinny. Walked right up to the door.

A feeling like a frozen arrow shunted down the Doctor's spine.

He couldn't be here. That was both a physical fact—he literally couldn't be here, as in, it was not possible—and an emotional one. If he spent another second here, his hearts would crawl up his throat and strangle him to death. He ran the rest of the way around the TARDIS. Then he hooked his foot on a rock and fell sprawling on the ground, knees scraped, head ringing. He ended up looking straight up Simon Smith's nostrils.

The boy stood over him. "Are you all right?"

"Unh," said the Doctor.

Another shadow loomed over the Doctor. A man held Simon's hand. The man was tall and thin and sandy-haired. He was about forty. He was trying to do stern, but his heart wasn't in it. He was mostly anxious but also very happy. Like he'd just run into a dear old friend, who he owed a great deal of money. The Doctor's own feelings drained down some inner crack, hopefully never to return—or at least, not until he got this lot sorted. Because this needed sorting in the worst way. This year tasted weird because it was weird. This wasn't just the wrong planet, or the wrong year. This was the wrong universe. And not just any wrong universe. The wrongest universe.

Rose's universe.

This was Bad Wolf Bay. And the man in front of him, wearing a funny green paper hat, was him. The other one. The metacrisis, half-human one. Let's call him John Smith—and why not? Smith was, no doubt, what he called himself. Rose, too, judging by the wedding ring. Rose Smith. Brilliant. Great. Brilliant. Not ghastly at all.

And their son. Their son.

"Well," said John Smith, settling his chin in his hand. "Isn't this wizard?"

#

"I don't—I would rather you didn't come in here," said the Doctor.

"Oh, would you?" John Smith pushed past the Doctor went into the TARDIS. He stood for a moment in the entrance and cocked his head. "Ah." Then he shook his head and strode up the walkway. "This is nice. I like it. The new design." He came over to the controls and brushed his fingertips over them. "Sim, don't touch."

Simon was just tall enough to look over the control panel. He looked like a kid who'd just been told that a present wasn't for him.

"The controls are so different," said John. "I thought I'd remember more. Can she hear me?"

The Doctor leaned against the door. He nodded.

"But it's not like it was with us," said John. He patted the TARDIS. "I'm sorry, old girl." His expression was wistful, but not miserable. "That's all right, though." He threw a grin over his shoulder. "You ought to see mine."

The Doctor stood up sharply. "You've got a TARDIS?"

"Don't be ridiculous," said John.

Simon bounced up and down on his trainers. "Can we go someplace?"

"No," said John and the Doctor together.

John settled down on one of the benches. Simon sat beside him, his feet dangling over the floor. John put a hand on the boy's clothespin shoulder. Simon was a pint-sized version of his father. They looked absolutely comfortable. The Doctor had to fight the feeling that he was evaporating.

"All right." John nodded. "Let's have it, then."

The Doctor came close to the control panel, feeling like he was sheltering under the limbs of a familiar tree. "Did you bring me here on purpose?"

"I didn't bring you here at all." John wagged his eyebrows. "Oooh, what now?"

The Doctor raised an eyebrow. "You come to Norway this time of year for the weather?"

"We come every Christmas," Simon declared.

"I don't think that's true." The Doctor came around the control panel and leaned against it. "Only the last two or three years, what? That's not bad timing. Considering your limitations."

"Yeah, I've still got it," said John, clicking his tongue. "It's trickier when you have to wait, though."

"Don't you get bored?" said the Doctor.

"Don't you get lonely?" John fired back. "I find ways to fill up the time, believe me."

"Me too. What am I doing here?"

"I don't know," said John. "But I bet it's something awful. Let's go find out. It'll be just like old times."

"I don't do old times anymore," said the Doctor.

"And yet here we all are," said John. He raised a finger. "Hold on."

John got up and walked to the front door. He opened the door and took a compact silver gun from the small of his back. The Doctor noted that he did it like it was a habit, smooth and quick. John opened up the weapon and tipped the bullets into his hand, dropping them into his coat pocket. He fired at the ground twice. Both times, the gun clicked empty. Then he took a handful of wet sand and worked it into all the mechanisms. The Doctor noticed that he'd done that before too. A familiar ritual. John threw the disabled weapon overhand into the sand. He slammed and locked the door. "Don't need that in here."

"That's littering," said the Doctor.

"Not in this universe," John replied. "They drag the beach once a week. Melt down the metal. They use it in the zeppelins. For the little parts. That was my idea."

The Doctor said, "Since when—"

"Not in front of my kid," said John. "All right?"

Simon looked up at both of them. Doing the math. Different universe, thought the Doctor. Different rules. Very different rules. Too different. The Doctor nodded.

John said, "We're going to the Tyler mansion. You know how to find it. Try to get us there tonight. I've missed Christmas the last two years in a row. I'd like to break the habit. Go on, then."

"Can I pull the lever?" Simon pointed. "It's that one, isn't it? The big lever, there."

John and the Doctor exchanged a glance.

"Course you can," the Doctor told Simon. "What d'you think it's there for?"

Simon came over to the big lever. It was too tall for him; John lifted him up. "Now remember," John said, "it takes a bit of oomph. It's like the game we play at home with the SIDRAT. You can't just pull it. You have to commit." Simon didn't have any problem following instructions. The Doctor was barely able to get the coordinates in before the boy threw the lever with every ounce of his strength.

The TARDIS had never been to the Tyler mansion, but the Doctor had. Anyway, it had never been that difficult for the Doctor to find Rose. It was second nature. Literally.

#

The TARDIS flashed out of the vortex and back into realtime.

Simon's face was pale, but he grinned. "Blimey!"

John sighed. "Don't swear."

"But that was amazing." Simon jumped up and down, full of energy. "The SIDRAT is rubbish compared to that. She's really alive, isn't she, Doctor? Didn't you feel it, Dad?"

"Yes." John looked a bit shaken himself. He put a hand on the control panel to balance himself. "I felt it."

"I can't wait to tell Tony!"

"Go on, then." John cuffed him, gently. "You're getting underfoot anyway."

"I bet you could go anywhere in this thing. Anywhere at all."

John set his jaw. "Yeah, it's like every-flavor beans."

Simon snickered. "You mean you could go someplace vomit-flavored?"

"I have done," said John. "Ask your mother."

The boy zipped out the front door. Then he came bounding back in. He saluted the Doctor. "See you later."

"I'm sure of it," The Doctor murmured.

John looked at him sharply, and the Doctor raised two fingers and shook his head one millimeter. I won't take him. There was no way on Earth or Heaven that the Doctor would have that boy in the TARDIS again. First, it would violate the Doctor's new rule against houseguests. Second, Simon was at least one-quarter Gallifreyan, and the last thing the universe needed was a tiny Time Lord banging around. The Doctor was bad enough on his own.

And finally, it would break John Smith's heart. That was obvious.

The boy ran back out again, calling, "Don't go again without me!"

He slammed the door behind him.

"Perceptive boy," the Doctor observed.

"Bane of our lives," John agreed. "Took apart the remote control when he was three. Now the only news channels we get are from Skellrax Nine—and they're two years old." John gave a stage-sigh. "Still, I suppose we have to keep him now." He paused. "You know it's funny, I was just thinking. They'd be taking him for initiation about now. Back home. Can you imagine?"

The Doctor shook his head. "No."

The Doctor's initiation was still fresh in his mind, though it had happened more than a thousand years ago. You never forgot the Untempered Schism. It broke everyone. It was always here, always now, always just an unguarded thought away. It whirled away in your mind for the rest of your life. A Gallifreyan child would never become a Time Lord without looking into the Schism, letting it eat at the sensible parts of his soul. But there was still a part of the Doctor that was hurt, and regretted, and wondered: what if I hadn't?

Simon was safe from all that. Thank God.

John gripped his temples. "Look, if this is going to work, we have to get one thing clear. Right now. I didn't want to talk about it in front of Simon because he wouldn't understand. I don't want him to. Ever. But here it is." He took a deep breath. "I'm not him. And I'm not you. I'm not a bit the Doctor. I've learned a lot since the last time we met. Things you can't know. Human life…" He shook his head. "It's bigger on the inside. And my choices were—are—human choices. And that's all you have any right to expect from me. All right?" He planted his feet and lifted his chin.

Silence settled between them like an unloaded gun.

"Fine," said the Doctor.

"Good." John leaned forward and lowered his voice. He smiled. "Would you like to see the SIDRAT now?"

"Depends what it is."

John angled his head toward the door. "Don't worry. You're going to love it." John held the TARDIS door open. "Step into my parlor."

The Doctor stepped through, and John followed him. They were in a large cellar. Like a warehouse.

In the center of the warehouse was a circle of mirrors. There were twelve of them. Ten feet tall, placed at intervals. Like a clock. Or Stonehenge. They were all wired into each other with thick cables. And in the center of the circle was the TARDIS.

The ring of mirrors felt like a time-engine, or a paradox machine, but was neither. The Doctor didn't have a name for what it was. SIDRAT, then. Backwards TARDIS. The system was well-balanced and ran clean, with a solid thirty-second buffer. And it was dead on accurate. To the millisecond. The Doctor could feel it. The SIDRAT was twice as accurate as the TARDIS on her best day. Of course it was only about a tenth as powerful, but what it lacked in juice, it made up for in precision.

"Gorgeous." The Doctor, turned on the spot, his mouth slightly open. "Unbelievable."

John grinned. "None of your shoddy workmanship, either."

"Hey!"

"Don't get tetchy." John rolled his eyes. "I don't have build everything out chicken wire and popsicle sticks anymore. We've been working on it for almost a decade. You wouldn't believe the money. You're looking at a quarter of the Tyler inheritance here. Oh, you should hear Jackie talk."

The Doctor kept his hands behind his back as he walked the inner perimeter. He was trying not to disturb the balance; with the TARDIS here, there was going to be a lot of energy buildup. Enough to fuel a big jump—or a big bang. Best to be careful. "What's it for?"

John shrugged. "Rose and Mickey worked out the basics before I got here. Then I tuned it up and put it into alignment. Human technology with that little bit of Time Lord. It's good, isn't it?" John flicked one of the mirrors. It chimed like fine crystal. The Doctor felt the resonance pattern and shivered. John continued, "It's not really meant for travel. Can't send a person very far, and can't bring them back. We're mostly using it to repair the Wall."

"The Wall." The Doctor looked at himself in the mirrors and bit his lip.

"The boundary between your universe and ours," John explained. "You remember all the hopping we used to do. Canary Wharf. The big displacement. It left a lot of micro-tears in reality. Most of them open onto the Void, some to your universe, some to… other places. Of course we repaired the really big ones a long time ago. Now there aren't many left much bigger than a cat door. Some are small as a flea."

"Knitting the universe back up. That's delicate work."

"It keeps me out of trouble."

The Doctor scoffed. "Really?"

John smiled coolly.

The Doctor folded his arms. "It doesn't. Keep you out of trouble. Does it? Because things are still getting in. Or maybe falling in. And I don't mean me. Things that would make a family man carry a gun when he's out with his his seven-year-old son."

"Oh, that's been happening for ages." John waved the idea away. "Since the first time we came here. There's a hundred-pound bounty out if you bring the body of a Dark Thing to the Ministry of Dimensional Integrity. A hundred and twenty if it has teeth or claws. Don't look at me like that. We don't participate. When we catch them, we bung them back through the Wall. Simon can hit one with a tranquilizer dart from twenty paces. I doubt that's it."

"Then what's the problem?" The Doctor wondered. "Why am I here? Why on Christmas?"

It was a rhetorical question. The boundaries between universes, between timestreams, were thin on Christmas. All that psychic energy directed at one day was bound to loosen things up. It was one of the reasons the Doctor did Christmas all the time and never did, say, Palm Sunday. And this universe was already vulnerable. A lot more vulnerable than the Doctor had planned for. Canary in the coal mine, this universe. Always had been. What happened here today could happen everywhere tomorrow.

"Feel free to let me know when you've figured it out," said John.

A familiar voice echoed down the stairwell. "John?" Both men froze, for different reasons.

"Oh, here we go," said John, between his teeth. He looked to the heavens.

The Doctor pivoted and headed back to the TARDIS.

John caught his elbow. "Don't you dare."

Rose came down the cellar stairs, talking all the while. "I didn't expect you back so early. Look, a check came for you from UNIT. Christmas bonus, I think. I know you don't want a salary, but they keep insisting. We can send it to Oxfam if you want. I don't care. And the wards keep going off. I don't think it's an incursion, I think it's just this snow. But you might want to check the traplines."

John kept a firm grip on the Doctor's elbow. "Sure. Send it to Oxfam. I don't care either."

"And you'll do the traplines? Tonight?"

John didn't respond.

Rose said, "It's a mess down here. Where are you, anyway?"

"The SIDRAT," called John. "Inside the matrix."

"That old thing. What're you doing in there? You know it's dangerous."

The Doctor arched an eyebrow. Dangerous?

John grimaced and shook his head. Not a big deal. "I think you should come in here."

She softened her tone. "You all right?"

The Doctor was not all right. He thought he might pass out.

John tapped his foot. "In your own time, Rose."

"All right. Hold your horses." She inched between two of the mirrors. She held a thick manila envelope in one hand. "Look, I didn't want to spend Christmas Eve alone, so I invited a few—oh. Who's—oh."

She'd seen the TARDIS. She went stock-still, and all the blood drained from her face. She tried to speak and failed.

"Now, Rose," said John, trying to calm her.

She turned to him, her eyes blazing.

John raised his hands in a gesture of surrender. "Just listen. I didn't call it here. I wouldn't have the first clue. You know that. I don't even want it here. Not in our house. And you know that." He paused. "And it's Christmas."

"Yes." She had to force the word out. She cleared her throat. "Yes, of course. Right. Christmas." She seemed to catch up to the moment. She put herself together and looked straight through the Doctor. "I suppose they have been a bit quiet lately, our Christmases. Why don't you come up, Doctor? We're having a little get-together. You'll get a real kick out of the guest list." She glanced at John. "All our friends are coming."

"Oh, perfect," John burst out.

"Oy, don't blame me. You didn't tell me you were coming home! And you didn't tell me you were bringing him." She kicked at one of the mirrors, throwing it out of alignment. The whole system twanged. There was even a sympathy moan from the TARDIS.

Rose took a breath. She spread her hands. "It's fine. It's fine. I'm sorry."

"I'm sorry," said John. "You're right. I should have warned you."

"Yes. But I'm fine." She ran into his arms. "I'm glad you came back." John hugged her. He looked like the cat who'd got the cream.

The Doctor stood to the side, feeling about as alone as he'd ever felt in his whole life. Letting John go, Rose reached out and squeezed the Doctor's hand. It startled him quite badly. Rose noticed. Well, she would. He'd just about jumped out of his skin.

"Let's start again," Rose said. "I'm glad to see you, too. 'Course I am. But I wish you weren't here. Because your being here means we're all in danger."

The Doctor nodded. "I think that's probably true."

Rose drew herself up. "But if we are in danger, then it's good. I don't know how it's possible, but it's great that you came. And we shouldn't be afraid of each other. We don't have time for it." She tossed her head. "Come on up. I'll show you the house. And I won't surprise you. It's a small party but you know everyone who's coming. Sort of."

The Doctor bit his lip. "What does that mean, 'sort of'?

She ticked the guests off on her fingers. "The heads of UNIT and Torchwood. And the President, of course."

"Right." The Doctor nodded. "And who're they, when they're at home?"

"Well," said Rose. "Respectively, that's this reality's Martha Jones."

John piped up, "And our Donna Noble."

"And our Harriet Jones," said Rose.

"You see," said John. "As soon as we settled in we got the band back together."

"We had to," said Rose. "Right away. The Wall is so vulnerable. And this reality hasn't got a Doctor."

At that point the Doctor turned around, got into the TARDIS, zipped off to the other end of the Universe, and started a new life as a turnip farmer on the Lost Moon of Poosh. He was a lot of things, but he wasn't a fool.

Oh, who was he kidding?

Of course he was.

And who didn't want this, anyway? Christmas with the family.