Two apparently respectable businessmen, running an electronics factory, are investigated by a journalist called Simon King. The businessmen turn out to be far from respectable and the journalist, they discover, is not a journalist. Who is Simon King, or rather, what is he?

Every war has a flashpoint, a fuse, a detonator—something, however small, that triggers it. In 1914, it was an assassin's bullet at Sarajevo. What could trigger an atomic war today? The Centaurans think they have the answer. And Simon, of all people, appears to be helping them...

Three scientists are mysteriously lost on a sledging party that set out from a polar research station.

The madman lives in a No-Man's-Land a borderline between fantasy and reality... where the real becomes unreal, the unreal real, and life itself a waking nightmare. Simon finds himself living in such a nightmare. Has he gone mad or is he merely suffering from temporary delusions? Above all, why should he want to kill a perfect stranger?

Sir Charles Munday is the richest man in the world. Might there be a Centauran plan to murder him?

Mary, visiting a village where she stayed as a child, finds that the woman who used to look after her, Hannah Webley, is now regarded as a witch by the superstitious villagers and Mary herself is soon caught up in the ensuing witch hunt. (The episode was cancelled the night it was due to air—13 October 1969—and replaced by a documentary on Ronnie and Reggie Kray, who, earlier that day, had been refused leave to appeal against their prison sentences. For unknown reasons, it was never rescheduled, remained unscreened, and was subsequently wiped from the BBC Archives.)

143 people in one small seaside town commit suicide by drowning. Or were they under some strange and alien influence? Simon decides they probably were...

In a period of student riots, strong calls for a return to 'law and order' are made by General Falcon, a blood-and-guts commander of the Korean war. Suddenly, he starts to emerge as an important political figure capable of swaying public and government opinion during an international crisis. Such a man, Simon decides, is dangerous.

When adults start acting childishly, it is no surprise to Simon. By his standards, most people are childish. However, when they start acting childish even by their own standards—when a grown man plays hopscotch and another falls off a rocking horse—something must be wrong. But can there be any connection between childish behaviour and the Centauran plan to take over the Earth? It seems unlikely, but Centauran plans frequently do. Until they start to work...

A deadly new germ gets loose at a biological warfare laboratory. Can an antidote be found before the germ spreads into a killer plague?