The Doctor and Sarah return to Earth in the present day to find a strangely deserted village and woods stalked by white-clad figures.

The Doctor suspects Crayford brought something to Earth in his rocket, as he and Sarah find themselves hunted by UNIT.

The Doctor is captured by Styggron and left to die in the destruction of the fake village but Sarah escapes from the disorientation chamber to try and rescue him.

The Doctor and Sarah reach Earth and try to warn the research centre about the Kraal invasion before Styggron unleashes his virus.