The Doctor and Jamie enlist the help of UNIT to rescue Zoe and Isobel before trying to find out what Vaughn is really up to.
Quest roles:
Nicholas Courtney(Brig. Lethbridge-Stewart), Kevin Stoney(Tyrum), Pat Gorman(Pilot), Sheila Dunn(Petra Williams), Sally Faulkner(Isobel Watkins), Peter Halliday(Soldier), Edward Burnham(Professor Kettlewell), Edward Dentith(Major-General Rutlidge), James Thornhill(Sergeant Walters), Robert Sidaway(Captain Turner)