The Doctor and Adric learn from the wizened Keeper of Traken that a great evil has come to his planet in the form of a Melkur - a calcified statue. The Keeper of Traken is nearing the end of his reign and seeks the Doctor's help in preventing the evil from taking control of the bioelectronic source that is the keystone of the Traken Union's civilisation.
Tom Baker
as The Doctor
Matthew Waterhouse
as Adric
Sarah Sutton
as Nyssa
Geoffrey Beevers
as Melkur / The Master
Anthony Ainley
as Tremas / The Master
Sheila Ruskin
as Kassia
Denis Carey
as The Keeper
John Woodnutt
as Seron
Margot Van der Burgh
as Katura
Robin Soans
as Luvic
Roland Oliver
as Neman
Liam Prendergast
as Foster
