The Doctor and Romana arrive on the marsh moon of Delta Magna in search of the next segment of the Key to Time. They are caught in the conflict between the native Swampies and the crew of a chemical refinery. The presence of a gun runner complicates matters; to make things worse, the Swampies intend to awaken Kroll, the giant god that lives beneath the swamps.
Tom Baker
as The Doctor
Mary Tamm
as Romana
Neil McCarthy
as Thawn
John Abineri
as Ranquin
Philip Madoc
as Fenner
Glyn Owen
as Rohm-Dutt
Carl Rigg
as Varlik
Frank Jarvis
as Skart
John Leeson
as Dugeen
Grahame Mallard
as Harg
