The Brigadier has recaptured Stangmoor but the Master still has control of the Thunderbolt and the Doctor must find a way to stop him and destroy the Keller Machine.
Quest roles:
Richard Franklin(Mike Yates), Nicholas Courtney(Brig. Lethbridge-Stewart), John Levene(Sergeant Benton), Dave Carter(Sergeant Duffy), Roger Delgado(The Master), Michael Sheard(Laurence Scarman), Martin Gordon(Prison Officer), Neil McCarthy(Thawn), Patrick Godfrey(Major Cosworth), Bill Matthews(Prison Officer), Barry Wade(Prison Officer)