Parts: 1 (90-minutes)
Writer: Terrance Dicks
Airdate: 25 November 1983
Production Code: 6K

Doctors: first, second, third, fourth, fifth
Companions: Susan, Jamie, Zoe, Liz, Sarah, K-9 mark three, the second Romana, Tegan, Turlough

Megalomaniac of the Week: the Master
Creature Feature: Daleks, Yeti, Cybermen
Special Guests: the Brigadier, Yates, the Time Lords

Story: On holiday to the tranquil Eye of Orion with Tegan and Turlough, the Doctor suffers a twinge of "cosmic angst"...but soon, the twinge grows stronger and begins to cripple him. Huge chunks of the Doctor's past are being ripped away, and unless he can contact his other selves, he will be destroyed.

But the Doctor's past selves have disappeared from the timeline entirely. Each has been snatched by a tumbling black obelisk, and relocated to the Death Zone of Gallifrey. An entertainment area used by the ancestors of the Time Lords, the Death Zone is surrounded by an impenetrable force field. In the center, the Dark Tower of Rassilon. The Doctors, along with several companions, must make their way to the Tower while navigating the dangerous terrain of the Death Zone.

But how have the Doctors been brought to the Death Zone, and who is responsible? The fifth Doctor suspects that someone has acquired control of the outlawed Time Scoop - and to do that, they would have to be very high-ranking indeed. If the Doctors succeed in reaching Rassilon's tomb within the Tower, the traitor will have access to Rassilon's ultimate gift...and if that happens, will the universe be safe?