Parts: 1 (8-minute)
Writer: Steven Moffat
Airdate: 16 November 2007
Production Code: n/a
Story: Travelling alone once more, the Doctor dematerializes the TARDIS from Earth, but the ship is soon buffeted by a strange force. When he examines the TARDIS console to determine the cause of the anomaly, he bumps into an unexpected visitor - his fifth incarnation. While the tenth Doctor marvels at the sudden appearance of his previous self, the fifth Doctor realizes that the TARDIS is malfunctioning, and unless the two of them can join forces to stop it, an imminent explosion could rip a hole in the universe.