With Tegan and Richard under alien control, and the manor sealed against anyone leaving or entering, it's a question whether or not the Doctor can get to London before the Terileptils release their improved strain of black death upon the world.
Quest roles:
Matthew Waterhouse(Adric), John Savident(The Squire), Michael Robbins(Richard Mace), Anthony Calf(Charles), Michael Melia(Terileptil)