Picking up a distress call from the edge of the known universe, the Doctor and Sarah Jane find themselves on Zeta Minor where a geological team has run afoul of some strange goings on...
Tom Baker
as The Doctor
Elisabeth Sladen
as Sarah Jane Smith
Frederick Jaeger
as Sorenson
Ewen Solon
as Vishinsky
Prentis Hancock
as Salamar
Graham Weston
as De Haan
Louis Mahoney
as Ponti
Michael Wisher
as Morelli
Terence Brook
as Braun
Tony McEwan
as Baldwin
Haydn Wood
as O'Hara
Melvyn Bedford
as Reig
