The Allen family didn't have ordinary Christmases.

It was 1910, and on Christmas Eve, as they had done on Christmas Eve every year, they packed up their things, and left their home. Mr. Jeremiah Allen had had an eccentric grandfather who left him a stately home on his death, despite the fact they had never met. Jeremiah knew it was the perfect place to spend Christmas, although the rest of his family didn't always agree. It was a big, cold and empty house, often isolated due to snow storms.

But Mrs Elizabeth Allen knew that it made Jeremiah happy and so she agreed to go, year in, year out. Their children had grown up with the yearly festive trips, but as they had got older, their enthusiasm had undoubtedly waned.

The eldest, Jonathan Allen, and the youngest, Isabella Allen, who preferred Jonny and Issy anytime when they were not with their parents, didn't really understand why they couldn't just spend time at home. Jonny had moved out of his family home three years ago, and Jeremiah and Elizabeth had expected Issy's long-term gentleman-friend to propose to her for the majority of that time too. They had lives of their own, and no time to be trekking to an almost-abandoned part of the country in the name of 'tradition'.

But they went, and they arrived, and they gathered around the table for their first meal. Jeremiah used the time to ask Jonny and Issy various questions about their lives – generally focussed around Jonny's employment and Issy's not-yet-fiancée. It was tiring for them both.

The most tiring thing, however, was the fact that every single member of the family was lying through their teeth the entire time.

They all hoped that vague, imprecise answers would be enough to stop them tangling themselves up in the stories they had been inventing on their way to the house. Each of them knew that they must keep their lies untold, at all costs.

All they had to do was get through Christmas, and then they could go home, and back to their lies.

But then there was a knock at the door. It was the only knock at the door the Allen's had ever had in the many years they had been at this house.

Jeremiah answered it, eager to tell whoever it was that they were busy and it was Christmas, so could they please come back, maybe on Boxing Day?

When he opened the door, he saw a short man, the falling snow filling the brim of his hat. He lifted it and smiled. He had a stubbled face, and short, messy, dark hair. He was wearing a cream suit and chequered trousers.

"Good evening," he said in a quiet, Scottish accent. "May I come in?"

Jeremiah tried to explain to the man that it was Christmas and he was with his family. The man didn't move.

"It's an important matter," he said. "I won't keep you for long."

Jeremiah was finding it difficult to say no. After a moment's hesitation he moved, opening the door wider, and allowing the man entry.

"What's your name?" Jeremiah asked him, as the man removed his hat and dusted the snow from it.

"A very good question," the man said. "You can call me the Professor, perhaps." There was a strange smile on the man's face. Wistful, Jeremiah thought.

"What can I help you with?"

"Are your family through here?" The Professor, without waiting for a response, moved out of the hallway and through the large double doors to the dining room.

Elizabeth, Jonny and Issy turned to see the new arrival.

"Hello," Elizabeth said, standing and walking over to the man. "Can we help you?"

"I'm the Professor." He rolled his 'r' a little as he spoke.

"Elizabeth Allen. What can we help you with?"

"It's quite a serious matter I'm afraid." He stopped, noticing the remnants of food on the table. "Oh I'm sorry, I'm interrupting your dinner."

"It's fine, you said it wouldn't take long, so," Jeremiah awkwardly moved into the room and stood in front of the man. "Who does it concern?"

"Have you been down to the village nearby?" The Professor asked.

"Um, only a few times, over the years. Not recently, though."

"Interesting. They suggested I come up and speak to you."

"Oh?" Jeremiah said, anxious. "What about?"

"Someone's gone missing."

"Oh dear," Elizabeth said. "That's terrible."

"Who was it?" Jonny had spoken this time. The Professor looked at him.

"How old are you?" The Professor asked.

"Twenty-one."

"He was your age. His name was Isaiah Jones." Although no one reacted to hearing the name, the Professor was certain that it had struck a chord, in some way, with all of them. Jonny's eyes had subtly moved to the ground, Jeremiah had stiffened, Elizabeth had moved her hands together. The Professor turned to see the only person in the room who hadn't spoken – a girl of about eighteen or nineteen. He hadn't realised she was there at first. Her eyes were fixed on him.

"I've never heard of him," Jeremiah said.

"What did you say your name was?"

"Jeremiah, Jeremiah Allen."

"This is your house?"

"Oh no, we come up here. An eccentric Uncle left it to me, I'd never even met him. We spend Christmas here."

"How lovely," the Professor fell silent, and wandered a little further into the room. He warmed his hands by the fire. "I'm just trying to get Isaiah home. Find out any information."

"Was he seen coming up here?" Issy spoke for the first time.

"He was last seen leaving the village in this direction. That was last night."

"How terrible for his parents," Elizabeth said. "But I'm afraid I don't know why anyone would suggest you come up here."

"Do you have a picture of him?" Jonny asked. The Professor turned to face him. "I'm good with faces."

"Yes, of course." The Professor moved away from the fire and reached into an inside pocket of his jacket. He drew out a photo, and showed it to Jonny. "Do you recognise him?"

"No, I don't actually. He looks so young."

"Let me see," Jeremiah stepped over to Jonny, but the Professor put the photo away.

"One person at a time, if that's okay."

Jeremiah stepped back, disgruntled. He looked to Elizabeth. The Professor watched their silent exchange. Elizabeth seemed confused. Her hands were still clasped together, her fingers interlaced.

"None of us recognise the name, and if you want show us his picture…" Jeremiah began.

"I'm not quite finished yet," the Professor said.

"It is Christmas Eve," Elizabeth said, "we'd like to carry on with our evening."

"Would you?" The Professor said. He cast his eyes towards the table. "This isn't a lot of food."

"Well, we were just finishing," Jeremiah said.

"But there wasn't a lot to begin with, was there? Saving your appetites for tomorrow?"

"That is the main event."

"Yes! Isn't it just. Although, I've often thought that Christmas Eve was just as lovely. Gathering together in anticipation. It has such a lovely sense of tradition about it, doesn't it?"

"That's why we come up here."

"It really is a lovely house. May I see some more of it? And then I'll leave you be."

Not really knowing what to say, Jeremiah looked again to Elizabeth, and then turned to the doors. "Of course. A quick tour."

"Thank you," the Professor said, smiling at each of the family in turn as he followed Jeremiah out of the room.

"We don't use much of the house, really, so a lot of the other floors are essentially closed off."

The Professor took no notice of this. While Jeremiah walked past the staircase and towards another room on the ground floor, the Professor made his way for the stairs.
"I'm afraid you can't go up there, Professor. It's awfully dusty, if nothing else." Jeremiah frantically made his way up after the Professor, but the little man was too quick for him, and was soon strolling along the first floor balcony.

"What beautiful wood," he said, "but I'd've thought you would've hung some paintings up."

"There were some when we arrived, but we took them down. My wife didn't like them."

"Does it make a difference, if you never come up here?" Suddenly, the Professor had darted into one of the rooms.

Jeremiah had never seen inside it before. It was empty, laced with cobwebs and dust. The Professor strolled over to the windows, and cleared one with his sleeve. He peered out.

"It's a beautiful night."

"Yes, it is," Jeremiah said.

"How did you arrive here?"

"Carriage."

"Did you have a driver?"

"No, no that's left up to me."

"Do you not have to look after the horses?"

Jeremiah realised, to his astonishment, that he didn't have an answer. In fact, he'd never really thought about the horses. "I'll go out and see to them when you leave," he said.

"That could be difficult," the Professor said.

"What do you mean?"

"Well, they're not there."

Jeremiah hesitated, and then moved to the window. He peered down at the gently falling snow and the courtyard. There was no sign of the carriage, or any horses. The snow had even covered their tracks.

"Still, at least it's saved you a job!" With that, the Professor left the room.

"Who do you think he is?" Jonny asked his mother, peering out of the dining room doors.

"He's gone upstairs."

"Well I'm sure your father will ensure we're rid of him soon enough."

"He's definitely picked his moment."

"I just hope that poor boy's okay. It's a cold night, I hope he's found some shelter somewhere."

"Maybe he's found it here," Issy said. Jonny and Elizabeth turned to look at her. "Maybe he's hiding in one of the rooms!"

"Don't say things like that, Isabella."

Issy fell quiet, and Elizabeth turned back to Jonny. "What a strange man. I wonder what qualifications he has."

"He's a Professor."

"Why is a Professor investigating a disappearance?"

"Maybe he liaises with the Police," Jonny suggested.

"He didn't look very presentable. Why would the people in the village tell him to come to us? Something doesn't make sense about this."

"Please, Professor," Jeremiah said across the hallway. The Professor was now hastily entering and exiting every single room. He seemed to be looking for something, but he didn't spend enough time in each room to look properly.

Until, eventually, he stopped. Jeremiah caught up with him, and peered inside. It was the room the family had put all the paintings in when they arrived. The Professor marched over to them, and begin flicking through.

"You took down a lot."

"Yes, well, there were a lot hanging up."

"Curious," he said, still searching. "Tell me about your Uncle, Jeremiah."

"Well, I don't have a lot to tell. I didn't know him, and the news came out of the blue about his death, and indeed, this house."

"What's the house called?"

"It's called The Threshold. I always thought it an odd name, I don't know why it wasn't named Cooper House."

"Why would it be called that?"

"Well that was my Uncle's surname."

The Professor stopped searching and turned. "Your Uncle didn't have your surname?"

"No? Is that unusual?"

The Professor didn't answer for a while, and eventually smiled. He began walking out of the room. "I must go and apologise to your delightful family for taking up so much of their time."

"He's coming back," Jonny said, before moving quickly away from the doors and taking a seat. He and his mother sat opposite each other. Issy was tapping impatiently on the wood of the table.

The Professor walked into the room, already looking like he was prepared to make a speech. Jeremiah dutifully sat down at the table, although wasn't quite sure what had compelled him to do so.

"I'll be going soon, I wanted to thank you for your hospitality. You've all been very gracious."

"Well, we hope we've helped in some way," Elizabeth said, although completely sure that they'd done nothing of the sort. Issy stopped tapping on the table.

"Oh, very much so. A very interesting evening."

"I'll show you out," Jeremiah stood from his chair.

"Oh no, no need." The Professor turned to leave, and then stopped. "Where's your daughter gone?"

"Well she's…" Jeremiah turned to indicate Issy. She wasn't there. Elizabeth and Jonny looked to the seat she'd occupied, and couldn't see her.

And then they blinked, and Issy was back.

"Well I'm here," Issy said, holding her hands out as if it was the most obvious thing in the world.

The rest of her family said nothing, and turned to face the Professor. He smiled. "Perhaps you'd like me to explain."

"I'm here, I'm fine," Issy insisted. The rest of her family were staring at her, open-mouthed. Sometimes, when they blinked, and shut their eyes for the smallest time, it was as if she wasn't there at all. And then she'd speak, or shuffle on her chair, and suddenly, she'd return. Like she'd never been away.

"I don't understand…" Elizabeth said.

"Neither do I, entirely," the Professor said. "I came here looking for a missing boy, and all we've discovered is a vanishing girl. Not your usual Christmas Eve." He'd rolled his 'r' once again.

Jonny watched him carefully. This strange man was beginning to enjoy this, finding a relish in the ability to take control of the room, to investigate whatever was going on with Issy.

"What's wrong with her?" Jonny hadn't wanted to ask the question, but despite his suspicions of this man, his fear of him, he'd engendered a strange sort of trust.

"A perception filter," the Professor said.

"A what?" Jeremiah asked.

"It disguises something, or someone, in plain sight. It shifts your focus a little so while you know they're there, you can never quite see them. Unless they make themselves known."

"But I'm always here! Where else would I be?" Issy protested. She stood, and made her way out of the room. "I'm going to my room, come and find me later when you've all calmed down."

And then her family blinked, and she was gone.

"Doctor, what on Earth is happening?" Elizabeth asked.

"You called me the Doctor," he said, looking into Elizabeth's eyes. "I never said that was my name."

"You… you told Jeremiah, when you arrived."

"He said Professor," Jeremiah said, his voice fretting. "He's never called himself the Doctor."

"Implying we've met before," the Professor – the Doctor – said, another smile on his face.

"It seems there's more than one mystery to solve here."

"What was going on with Issy, how could she… do that?" Jonny asked.

"You have a great number of stories on this planet concerning the existence of ghosts. There are certain planets in the universe that have perfected the art of living forever. Those two statements come to the same end. Imagine if you were from a planet where death was not a common concept, and that it was instead replaced by existence through perception filter. The perfect way to deal with grief – you only see someone when you really need it. Or when they do."

"Another planet?" Jonny said. His eyes were brimming with tears. "She's my sister, I grew up with her…"

"I don't believe you did, but that's another story."

"How would she have come here?" Elizabeth asked. "If she is as you say… If she's travelled here."

"This house is called The Threshold. I think it attracts lost souls. People who are not quite one thing or another."

The Professor let his words settle. Jeremiah, Jonny and Elizabeth slowly looked at each other. They weren't sure how, but they understood exactly what he had meant. All of their lies, the lies they knew they had to keep secret at all costs, but had never quite been able to pinpoint themselves.

They were the lies. Their very existences weren't real.

"Elizabeth, shall we start with you?"

The Professor took them upstairs. As they went, Elizabeth called out for Isabella, but she was nowhere to be seen. The Professor assured them that they would see her when she was ready to be seen, and took the remaining members of the family into an upstairs room.

Elizabeth saw all the paintings that she'd insisted were taken down on her arrival. The Professor knew which one he needed, and immediately strode over to it.

"Would you like to see?" The Professor asked.

Elizabeth looked at her family, and then, slowly, walked across the room. The Professor lifted up a heavy gold frame, and invited her to see what was on the other side of it. He shielded it from Jeremiah and Jonny.

Elizabeth sobbed when she saw the canvas.

"What's on it?" Jeremiah stepped forward. Elizabeth stared at the painting, and then looked up at her husband. "Elizabeth?"

"Come and see."

He did as she said, and stepped round to see the painting. He was surprised. There was nothing on it. There were colours – a dull green background, like a piece of velvet. But there was nothing in front of it.

Then he realised. He looked at Elizabeth. He tried to take her hands but she had clasped them together. Tears rolled down her cheeks, and Jeremiah wiped some of them with his thumb. He looked at his thumb, and saw that not only was it wet, but it was smudged with the colour of Elizabeth's cheek.

"The frame says that this painting of Elizabeth de Luca was completed in 1721. I imagine, a portrait of a woman who was sat with her hands clasped together." He paused, let his words settle again. "I remember 1721," the Professor said. "And I think you remember me."

"Why am I here?"

"Because the Threshold needed to complete it's perfect family."

"Where do we fit into that?" Jeremiah looked at the Professor, trying to keep his anger suppressed.

"You're dead, Jeremiah." The Professor didn't let his words settle this time. "I don't know when you were killed, but I suspect it was in this house, and this house preserved you. It's very good at that."

"But… we only come here once a year, it's not my house!"

"No, it's not your house, but nor was it your Uncle's. I don't know if he even existed, he was just the story you've been given to make your new reality seem bearable."

"If this house brought us here, Doctor, what happens when we leave it?" Elizabeth asked.

"I don't believe you ever do. There's no carriage outside. I think you go to leave, on Boxing Day, every year, and then you come back immediately, and it's Christmas Eve."

"But I… the memories I have are real!" Jeremiah shouted.

"Maybe the real memories of a family who lived here once? That the Threshold is trying to recreate? Who knows?" The Professor shrugged with a smile. "I sensed something strange in this house when I was told about Isaiah Jones. I've found something bigger than I imagined."

"What about him, then?" Jonny had spoken from across the room. "What about Isaiah Jones? None of us recognised his name, you showed me a picture, I didn't recognise him."

"I showed you a picture of one of my friends," the Professor said. "Would you like to see a picture of the real Isaiah Jones?"

Jonny didn't answer. The Professor slowly walked over to him, and drew something from his inside pocket. He waited, and Jonny nodded. The Professor showed him what he was holding. It was the same size as the picture of Isaiah Jones, but it was a mirror.
Jonny stared at his own reflection, and looked up at the Professor, tears once again in his eyes.

"It's me?"

"You've been missing for a long time. The village talk about you every year."

Jonny didn't say anything, but soon his emotions overwhelmed him. The Professor stepped away from him, and Jeremiah and Elizabeth rushed over to comfort their son.

"So we… we're not a family?" Elizabeth asked.

The Professor said nothing at first, until a small, sad smile crept onto his face. "Well, I suppose, family is what you make of it."

"Will the house release us?"

"Maybe, if you want it to. I've opened up a dialogue. I hope it was listening." And with that, the Professor turned to go. "Merry Christmas."