Parts: 4
Writer: Johnny Byrne
Airdates: 31 January 1981 - 21 February 1981
Production Code: 5T

Doctor: fourth
Companions: Adric, Nyssa

Megalomaniac of the Week: the Master

Story: As the TARDIS approaches the Mettula Orionsis system, containing the Traken Union - a place of perpetual harmony - the craft is infiltrated by the Keeper of Traken, an elderly man hunched in his throne. The Keeper asks the Doctor for his help, as he foresees a time in the near future when the planet will be beseiged by a great evil.

Although most evil beings landing on Traken soon calcify and become part of the verdant Grove, one of the recent additions - called Melkur - has not followed suit. A tall statue that can neither walk nor speak, it is carefully tended by Kassia, soon to be wife of Tremas, one of the Consuls of Traken. Kassia is extremely surprised when, on the last day of her care for Melkur, he speaks to her. Melkur has a plan to take over the position of Keeper, and for that, he needs Kassia's help.

Despite Traken's reputation, the Doctor and Adric soon become mistrusted. Only through the aid of Consul Tremas and his sweet, scientifically-minded daughter Nyssa can they attempt to stop Melkur from controlling the vast power source available to the Keeper...but all is not what it appears.