Parts: 4
Writer: Robert Holmes
Airdates: 6 September 1986 - 27 September 1986
Production Code: 7A
Alternate Title: The Trial of a Time Lord parts One through Four
Megalomaniac of the Week: the Valeyard
Special Guests: the Time Lords, Glitz
Story: The TARDIS is snatched out of space and time to an enormous station. The Doctor emerges, suffering from a slight bout of temporary amnesia, to find a darkened courtroom and a man dressed in black who seems to be waiting for him. The lights come up and a regal woman enters - she is the Inquisitor, the man in black the Valeyard, and the Doctor is on trial. For the prosecution, the Valeyard attempts to prove that the Doctor is an incorrigible meddler in the affairs of others by presenting one of his recent escapades.
The Doctor and Peri visit Ravolox, a rainy planet which Peri finds similar to Earth. The Doctor senses a mystery - according to the TARDIS, Ravolox was destroyed by a fireball, yet the planet is covered in trees and other forms of plant life. The Doctor finds signs of habitation and investigates - and Peri uncovers an old sign for Marble Arch. Ravolox is indeed Earth, though how it moved so far from its original position, the Doctor does not know. Naturally, he decides to investigate.
Meanwhile, two con men - Glitz and Dibber - have come to Ravolox on a mission of their own, and they don't like having the Doctor and Peri around. But worse things are in store for everyone on Ravolox - the black light converter that powers an underground robot is badly malfunctioning, and if it blows up, it could take the entire universe with it.