Let’s start with a story.
March 1977. A nine year old Yorkshire lad by the name of Billy Hanshaw watches in horror as his beloved Leela gets her ankle savaged by a huge rat in the London sewers. “Shame that,” observes his father, “she’s got nice legs.” The closing theme bursts into life, and Billy realises he’ll have to wait a whole week to find out if the Doctor can rescue her.
Suddenly the room is filled by a strange groaning noise, the unmistakable sound of the TARDIS. Billy turns and watches as a middle-aged guy in a beaten leather jacket emerges from the blue box. Could this be a future incarnation of the Doctor?
“You wanna come with me?” he asks in a northern accent.
“Sure, where we going?” replies Billy in an even more northern accent, completely forgetting everything he should have learned from Charley Says.
“Into your future,” says the Doctor. “2014 to be precise. I’m going to show you your future self.”
“But I can’t cross my own time stream,” argues Billy. “It’s not the done thing.”
“Just pretend its an anniversary,” replies the Doctor. “It’s OK then apparently. Though personally I’m not too keen on the idea.”
And so the Doctor and Billy traverse time and space, coming to rest in a place known to the people of Earth as Cardiff. Emerging from the TARDIS, Billy gasps. It’s like a huge cinema, with a comfy looking sofa in front of the big screen.
“St. David’s Hall,” says the Doctor. “The world premiere of a new series of Doctor Who. The first time ever people get to see my twelfth self in action.” He nods across the room to a man and woman sat eating Revels. Take a look at them two. Recognise them?”
Billy looks intently, and suddenly the realisation dawns across his face. “It’s me!” he cries. “It’s me and Leela!”
The Doctor smiles. “Yes kid, you and Leela. Who’d have thought it, eh?”