On the lush planet Tigella, two opposing factions are divided over the usage of the Dodecahedron, an ancient and powerful artefact which provides the entire planet's energy. The Doctor is summoned to arbitrate the conflict, but the power-crazed Meglos intercepts the call and impersonates him in order to steal the Dodecahedron.
Tom Baker
as The Doctor / Meglos
Lalla Ward
as Romana II
John Leeson
as K9 (voice)
Bill Fraser
as General Grugger
Frederick Treves
as Lieutenant Brotadac
Edward Underdown
as Zastor
Jacqueline Hill
as Lexa
Colette Gleeson
as Caris
Crawford Logan
as Deedrix / Meglos (voice) (uncredited)
Christopher Owen
as Earthling
Simon Shaw
as Tigellan Guard
