Two-part telethon mini-story for Comic Relief 2011 in which the TARDIS materialises inside its own control room, and becomes stranded inside itself.
The Doctor: "The inside of the TARDIS is now joined to the outside of the TARDIS. It's worse than a time-loop - a space-loop. Nothing can enter or leave this ship ever again."
Actually it's even worse than that, as it then slips slightly forwards in time. Now when one of them enters the ship's exterior, they step through straight back into the same control room a moment in their own past. So Amy's self from a moment in the future suddenly bursts in through the doors, appearing to have just got this dynamic sussed, although the words that she uses muddy it a bit.
Amy Sr.: "Well, the exterior shell of the TARDIS has drifted forwards in time. If you step into the box now, you step inside the control room a tiny bit in the past."
Amy Jr.: "I don't understand."
Amy Sr.: (whispers)"Neither do I."
Amy Jr.: "But you just said it!"
Amy Sr.: "No, I'm just repeating it. I'm just repeating what I heard myself saying when I was standing where you are now and repeating it. I'm just repeating this too. And this. And this."
Amy Jr.: "Urghh, I still don't understand."
Amy Sr.: "You still don't."
As you can see, it's written by Steven Moffat.
The thing about telethon specials, is that they very rarely deliver on anyone's hopes. They're generally billed as though we will actually get a genuine new episode of the series that we watch and love, but very rarely does this ever seem to be the case. Typical shortcomings include turns to camera, celebrity guest-stars, and flat contradictions of continuity. Heck, they often don't even come with any credits on them.
Not so Space / Time. This is authentic Doctor Who start to finish, and stands up perfectly well as an entry into the canon in its own right. No-one puts on a red nose, or picks up a Pudsey, or is greeted by Terry Wogan walking on set at the end. It even seems to be take place between the episodes that were broadcast around it.
Well, the action inside the TARDIS does anyway.
At another point in the same Red Nose Day telethon, the Doctor did put in another appearance to plug what would be coming up later, but thankfully that's completely separate to the main story. In fact, his solitariness would place that visit at a different point in his travels, with a different looking TARDIS and no Amy or Rory. Towards the end of the farewell tour between The God Complex and Closing Time then. In fact, since his ship seems to have the same smoked-windows, I'd place this just before The Doctor Undresses.
It's worth noting that, unlike his other live appearances, Smith doesn't entirely win the battle to stay in character here. Thank God for the blustery precedent set by William Hartnell!
If you're trying to get someone interested in Doctor Who, but they're only willing to give it eight minutes, then Space / Time is probably the story to show them.
However please do be sure to explain that the TARDIS' exterior looks like a Police Box first.