When the Master steals the Time Lords' secret file on the Doomsday Weapon, they grant the Doctor a temporary reprieve from his exile on Earth to deal with the crisis. He and Jo arrive on the planet Uxarieus and become enmeshed in a struggle between an agrarian colony and a powerful mining corporation.
| Actor | Role |
|---|---|
 Jon PertweeThe Doctor | The Doctor |
 Katy ManningJo Grant | Jo Grant |
 Nicholas CourtneyBrigadier Lethbridge-Stewart | Brigadier Lethbridge-Stewart |
 Roger DelgadoThe Master | The Master |
| NNicholas PennellWinton | Winton |
| JJohn RinghamAshe | Ashe |
 David WebbLeeson | Leeson |
| SSheila GrantJane Leeson | Jane Leeson |
 Roy SkeltonNorton | Norton |
 Helen WorthMary Ashe | Mary Ashe |
| JJohn LineMartin | Martin |
| MMitzi McKenzieMrs. Martin | Mrs. Martin |
| JJohn Scott MartinRobot | Robot |
 Pat GormanPrimitive / Voice / Long / Colonist | Primitive / Voice / Long / Colonist |
| GGraham LeamanTime Lord | Time Lord |
 Peter Forbes-RobertsonTime Lord | Time Lord |
| JJohn BakerTime Lord | Time Lord |
 Bernard KayCaldwell | Caldwell |
 Morris PerryCaptain Dent | Captain Dent |
 Tony CaunterMorgan | Morgan |
| JJohn HerringtonHolden | Holden |
| SStanley McGeaghAlien | Alien |
 John TordoffAlec Leeson | Alec Leeson |
| NNorman AtkynsThe Guardian | The Guardian |
| RRoy HeymannAlien Priest | Alien Priest |