Air: Jan 1 1972. 4 eps.
UNIT has been sent to safeguard a peace conference. When suddenly guerrillas from a parallel world have come to assassinate a certain man. Where they come from is a time where the earth was ruined by a world war and The Daleks have taken over, they have traveled to this time to assassinate the very man that started the world war. Can The Doctor prevent his old foes from exterminating him?