When someone tries to assassinate diplomat Sir Reginald Styles, UNIT investigate the possibility his attacker came from the future.

Jo uses the guerrillas' time machine to travel to the 22nd century where the Controller tricks her into telling the Daleks where she's come from.

The Doctor forces the guerrillas to take him to the 22nd century where he is soon captured by the Controller.

The guerrillas infiltrate the Daleks' base to rescue the Doctor and Jo and ask them to return to their own time and alter history before the 20th century is plunged into a Third World War.