- Tom Baker
- Doctor Who / Narrator
- Lalla Ward
- Romana
- Christopher Neame
- Skagra
- Denis Carey
- Professor Chronotis
- Daniel Hill
- Chris Parsons
- Victoria Burgoyne
- Clare Keightley
- David Brierly
- K9 / Computer (voice) (as David Brierley)
- Gerald Campion
- Porter (Wilkins)
- Shirley Dixon
- Voice of Skagra's Ship
- Derek Pollitt
- Professor Caldera (episode 4)
- John Hallet
- Police Constable (episode 6)
- Graham Cole
- Krarg
- Harry Fielder
- Krarg Commander / Krarg 3 (uncredited)
- James Muir
- Krarg
- Lionel Sansby
- Krarg
- Ken Sedd
- Young Scientist
- Derek Suthern
- Krarg
- Reg Woods
- Krarg
