"So you're the Doctor?" Entis asked.

He nodded, "I am the Doctor."

"Oh, good for you, Doctor."

The Doctor glared at him, "What?"

Entis looked away, "Oh, nothing."

They were walking with Entis through his maze of a workshop, marvelling at the amazing amount of... stuff that he had hoarded, while the Doctor was spending his time by being indignant at Fenn's high-jacking of the TARDIS.

"What is all this stuff?" Amy asked.

"Scraps of technology from crashed ships, seized contraband, illegal weaponry from the black markets on Kelba-8... though don't tell the Proclamation about the last one," he added, glancing sideways at the Doctor.

"You keep illegal guns in the basement of the Intergalactic Police?"

Entis stopped and stared at Amy, 'I'm sorry, but who are you?"

"Amy Pond," she smiled and extended her hand.

"Nice to meet you, Amy Pond," Entis returned the smile and shook her hand, "I'm Entis Parkes."

"I know."

Entis paused in confusion for a moment, then continued leading them down the path between the mounds of scrap.

"Do you travel with the Doctor, Amelia Pond?"

It was Amy's turn to stop, "How did you know I was Amelia?"

Entis smiled and winked at her, "Lucky guess." Fenn grinned at him from behind Amy's back. Entis grinned back until they arrived at their destination, "Ah! Here it is!"

Fenn asked, "Here is what?"

"Take a guess."

They gazed at it in awe, and the Doctor stepped forward to get a better view, "Oh, that is beautiful!"

It was a massive steel box, twice as tall as the Doctor and about two metres wide. A small touch screen mounted to the front of the box scrolled through various bits of data. There was a small square door, about a foot wide and high. It was glass, or what looked like glass, with two metal latches keeping it shut. Inside the door was what looked like a hollow cylinder, rotating very slowly.

Entis shrugged modestly, "Well, I guess..."

The Doctor looked at him, "No, really, I mean it! That is beautiful. So simple."

Amy rolled her eyes, "Well, once you're finished falling in love with it, can you tell us what it is?"

Fenn nodded, "For once, I don't know what I'm looking at. Entis, what is this?"

"Multi-dimensional inter-universal trans-temporal energy signature locator," he rattled off, "or MITES locator, for short."

Amy rolled her eyes, "Which means what, exactly?"

This time the Doctor answered, "It's a tracker."

Fenn looked at Entis, "You can't find Hannah with a tracker, she's been erased from time!"

"No, no, Fenn, not that sort of tracker."

"What sort of tracker then?"

"An energy-signature tracker. It detects energy signatures from all times, dimensions and universes."

Fenn glared at him, "How does that change my point? She was erased from time. There's nothing to track!"

"The traces," the Doctor breathed.

They all looked at him, confused but sensing a breakthrough. Amy asked, "What?"

He looked at him, the spark of invention lighting up in his eyes, "The traces! Of course! Why didn't I think of that?" He looked at Entis, "You sir, are a genius. And coming from me, that's something."

Entis bowed, "Oh, I know."

Amy was still confused, "I'm sorry Doctor, but what?!"

The Doctor slowed a bit to explain, "People fall out of the world sometimes, Amy, but they always leave traces. Little flaws and images we can't quite account for. Clothing, books, half-eaten food, photographs..." he remembered Rory, and the sadness flashed across his face, just for a second, "rings. People die, or fall out of the universe... some more recently than others. And there are always a select few unlucky souls who are left behind to remember." He bowed his head.

Fenn looked at him, "Are you okay, Doctor? It's not..." she glanced at Amy, "It's not Rory, is it?"

He leaned on a nearby bench with one hand, "No, not Rory... it's just... Sarah Jane died, the other day, and talking about people we lose reminded me of her."

"But you've got the TARDIS... can't you just go and see her?"

The Doctor glared at her, "What has passed, has passed, and should not be touched again... simply out of respect."

Fenn nodded with understanding, and the eerie silence echoed hollowly in the empty space between them.

Amy turned to Entis, "So how does this thing work?"

Entis continued the explanation, "This machine tracks down the traces of those people who were lost, and the energy signature they have left behind. Because you might not know it, Miss Pond, but you are brimming with energy right now, and wherever you go you leave an imprint, for just a fraction of a second. Like a temporal fingerprint, a big ol' neon sign flashing 'AMY POND WAS HERE!'. Time travellers tend to have particularly distinctive signatures, because of their displaced temporal energy from the vortex, which makes them particularly easy to find. The imprints don't last long, but in the vortex a second can seem like two thousand years depending on your angle. The MITES locator tracks down the imprints and pieces them together to form a full impression of the person, like a jigsaw of trillions of atoms."

"Why do you need multiple imprints? Why not just one?" Fenn asked.

"Because it's incredibly rare to get a complete imprint- they're often incomplete; a puzzle missing a few pieces. You need more than one to make a full image."

"But that would just create an image, a template of Hannah's energy signature," the Doctor said, "You would need a full DNA reconstruction to provide a proper physical manifest."

Entis grinned, "Look to your left."

They turned, and saw what looked like a giant metal and glass shower cube with a computer tacked to the side of it.

Fenn smiled, "Now, I know what that is! That's a clone tube!"

Amy's eyes widened, "You use that thing to grow clones?"

The Doctor patted her back reassuringly, "Don't worry, Amy, in these times cloning is like getting your picture taken. Leaving your mark on the universe."

"But are they real? Like, actual clones?"

Entis was taken aback, "Well of course they're real! None of my work is less than top of its class, they're as real as they get! As much a human as you or me... well, you, at least. Your people are the original models. There's been a bit of genetic variation since then."

Amy shook her head, "This is so weird. It's like one of those sci-fi movies you see at home, with all of the people growing in tubes."

"Now, Amy, don't be rude," the Doctor cautioned her, "over a quarter of the human world's population now have had some type of DNA reconstruction. It's not something they like to share, but it's a fact of life nowadays."

Fenn's brain was ticking over, still staring at the clone tube, "So you're going to use the energy signature to construct an exact DNA composite replica of Hannah?" She asked Entis.

Entis's grin grew wider, if that were possible, "Yep, that's it! For all intents and purposes, it won't be a replica of Hannah, it will be Hannah. A collection of scraps of her life squished together to form a whole. All I need is a base signature to tell the computer what to look for- anything she owned would do it. It'll have traces of her on it."

Smiles faded all around. Fenn looked at him, "Something of hers? I don't know if anything survived the time energy." She glanced at the Doctor, who shrugged, "Don't look at me; I don't have anything of hers."

Fenn sighed and started patting down her pockets. "I don't think I had anything of hers on me; we didn't tend to borrow each other's-" she stopped, and pulled something out of the inside pocket of her coat. It was a disk.

Fenn stared down at it, "Now that's odd. I don't remember her giving this to me..."

The Doctor walked over to look at it but Fenn held it away, "Sorry, Doc, but you can't see this one. Spoilers."

The Doctor sighed with frustration, "You're not River, and I'm not Doc. Can you at least tell me what it is?"

Fenn grinned as she handed the disk to Entis, "The final disk of the fifth season of Doctor Who, detailing the three episodes The Lodger, The Pandorica Opens and The Big Bang. Normally I'd love to watch it again, but if you've just finished with Vincent, then it's your future and I can't."

There was silence again as Entis sat the disk in the glass-door chamber on the MITES locator.

"Okay," he said, "let's bring Hannah home!"