The Doctor and Jamie return to the IE factory in search of Zoe and Isobel, where they meet with Professor Watkins and fall foul of Vaughn.
Quest roles:
Nicholas Courtney(Brig. Lethbridge-Stewart), Kevin Stoney(Tobias Vaughn), John Levene(Sergeant Benton), Sally Faulkner(Isobel Watkins), Peter Halliday(Soldier), Edward Burnham(Professor Kettlewell), James Thornhill(Sergeant Walters), Robert Sidaway(Captain Turner)