The doorbell rings and dad, John and I take our seats. Mrs Hudson leads up the young woman we saw outside.
"Sherlock," she says, knocking on the open door. "A young lady is here to see you."
"That is quite obvious thank you Mrs Hudson," dad says, shooing her away and gesturing for the woman to sit down. "What's your name?"
"Wait," John says, sitting up straight. "I know you. You're Billie Piper - the woman from Doctor Who." He turns to us and shakes his head at our clueless faces. "She played Rose Tyler, one of the new companions." I nod. This is slightly weird - meeting one of the women who was in the TV show that we now know to be real. But Piper shakes her head.
"No, I'm not," she corrects. "I really am Rose Tyler. If you're familiar with the show then you'd know I became trapped in a parallel universe - this universe." John frowns.
"But didn't that world have cybermen and airships?"
"According to the show, yes it did," she replies. "But that's not how it played out in reality. But I'm not here about that. I need your help to find the Doctor."
"But as you know," I reply, "he's in the other universe."
"Not that Doctor, my Doctor." Dad and I look at her blankly so John explains.
"There was a regeneration which the 10th Doctor managed to siphon off his residual energy onto his cut-off hand, meaning he didn't have to change his face. This created a second Doctor, but this one was human." Rose nods in agreement.
"The other Doctor left us together in this world and all's been fine until a few weeks ago." She takes her phone out of her bag and hands it over to us so we can flick through her photos. "What do you know of the organisation Torchwood?"
"I know a bit about the TV show Torchwood," John says, sitting forward. "Is the one over here the same?"
"Similar," Rose replies. "No Jack, but the others are there. The reason I'm here is because we've encountered a weird scenario - unlike any of us has seen before."
"If you could be a tiny bit more specific," dad says, rolling his eyes.
"The best way I can describe it is ... supernatural."
"Sorry," I say, shaking my head. "Did you say supernatural? You mean like ghosts?"
"Ghosts," she repeats, nodding, "but also demons." I'm finding that slightly easier to believe after our incident with the Hound, but I'm still not convinced. "Torchwood picked up on a number of people who were going missing only to turn up again acting out of character. We thought alien possession, it's unlike anything the Doctor has ever seen. He and I started working the case together but now he's disappeared. My worry is he's being possessed. If that is the case, we're in a lot of trouble."
"So what do you need us to do?" John asks.
"Find him," Rose says. "He's gone underground and we've exhausted our resources trying to find him. I was hoping you could pick up on something we may have missed."
"What do you think," I ask, turning to dad.
"Not buying this supernatural thing," he replies, finishing with the phone and handing it back to Rose. "You saw what happened with the Hound - it was little more than a drug infused nightmare."
"But we need a case," I remind him. "The worst that could happen is we prove to a secret government agency that it is little more than a serial kidnapper." Dad considers this for a moment and I'm fairly sure he's just weighing up what he's going to tell Mycroft when we prove that one of his organisations are conspiracy theorists.
"We'll take the case."
"Fantastic," Rose replies, standing up. "I'll email you the files we have so far." She walks towards the door but stops before she passes through. "You guys realise you're book characters in my world?"
"Strange," I say, avoiding an answer. She nods.
"See you around, then," she says before continuing on out. As we hear the door close downstairs, we look at each other.
"Are we going to tell her we know the Doctor?" John asks after a minute.
"That's hardly relevant John," dad replies. "It would seem Moriarty has made his move after all."