After the TARDIS collides with a spacecraft delivering human tributes to the evil bull-like Nimon, the Doctor and Romana must stop the fearsome alien's quest to rule the galaxy.
| Actor | Role |
|---|---|
 Tom BakerThe Doctor | The Doctor |
 Lalla WardRomana II | Romana II |
 David BrierlyK9 (voice) | K9 (voice) |
 Graham CrowdenSoldeed | Soldeed |
| MMichael OsborneSorak | Sorak |
 Bob HorneryPilot | Pilot |
 Malcolm TerrisCo-Pilot | Co-Pilot |
| CClifford NorgateNimon (voice) | Nimon (voice) |
| RRobin SherringhamNimon | Nimon |
| BBob ApplebyNimon | Nimon |
| TTrevor St. John HackerNimon | Nimon |
 Janet EllisTeka | Teka |
 Simon Gipps-KentSeth | Seth |
 John BaileySezom | Sezom |