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
Lalla Ward
John Leeson
Bill Fraser
Frederick Treves
Edward Underdown
Jacqueline Hill
Colette Gleeson
Crawford Logan
Christopher Owen
Simon Shaw