The Doctor is sentenced to life imprisonment at a lunar penal colony while Jo encounters an old enemy.
Quest roles:
Roger Delgado(The Master), Karol Hagar(Secretary), Harold Goldblatt(Professor Dale), Madhav Sharma(Patel), Richard Shaw(Cross), Luan Peters(Sheila), Caroline Hunt(Technician), Laurence Harrington(Lunar Guard), Vera Fusek(President of Earth), Michael Hawkins(General Williams), Dennis Bowen(Prison Governor)