Parts: 4
Writer: Steve Gallagher
Airdates: 14 February 1983 - 23 February 1983
Production Code: 6G

Doctor: fifth
Companions: Nyssa, Tegan, Turlough

Megalomaniac of the Week: Black Guardian

Story: Under the guidance of the Black Guardian, Turlough attempts to remove a critical TARDIS system. His efforts cause the ship to destabilize, with parts dissolving into a colorful static as they begin to fall apart. Nyssa, trapped in her room, has nowhere to run - until the TARDIS locks on to the nearest spacecraft and a door appears through the static. Instructed by the Doctor to flee, Nyssa runs through it.

When the ship's instability settles down, the Doctor, Tegan and Turlough follow her through. On the other side of the door is a stark metal ship, apparently empty of passengers, with a disturbing skull motif on the walls. The Doctor finds Nyssa, but gets lost on his way back to the TARDIS; Tegan and Turlough likewise get lost trying to find the Doctor. Meanwhile, a pair of advance scouts for a raider vessel blast their way on board to steal the ship's cargo. When their ship abandons them, and they are unable to find the object of their mission, they attempt to hijack the Doctor's ship. He calls their bluff, and they agree to join forces.

Tegan thinks she hears Nyssa, calling for help behind one of the skull-bedecked doors, but when she pries it open, she is assaulted by several filthy hands clutching at her clothing. Then the ship approaches a station and prepares to dock. As a voice alerts the passengers to disembark before sterilization, the many doors on the ship begin to open, and moaning people shuffle out of them and along the corridors. One of the rebels realizes they have come aboard a leper ship, where everyone is destined to die. In short order, Nyssa herself contracts Lazars' disease...and for the mistreated, unwanted lepers, the only certain cure is death. But even Nyssa's plight pales in comparison to that of the rest of the universe; for if the poorly-maintained fuel reactors of Terminus explode, the resulting explosion will bring about an early oblivion...for everything.