The Mysterons threaten to destroy London and a truck carrying an atomic device goes missing and is hidden somewhere in the city. The only clue to its whereabouts is the truck driver, found unconscious in the street.

Following the latest Mysteron threat, Captain Scarlet is dispatched to supervise security at the International Air Conference at Glen Garry Castle in Scotland.

The Mysterons threaten to obliterate the continent of North America, but Spectrum is left without its number one agent when Captain Scarlet is dismissed for gambling offenses.

The Mysterons take control of an experimental super-tank in an attempt to assassinate the Supreme Commander of earths armed forces.

When the Mysterons threaten to kill one of the Angels, Captain Scarlet and Captain Blue are sent to Paris, where Destiny Angel is on holiday, to escort her back to the safety of Cloudbase.

The Mysterons engineer the launch of a Variable Geometry Rocket from Base Concord and their agent, Major Reeves, escapes with the destruct mechanism and target information.

Captain Scarlet and Captain Blue are sent to observe an operation to obtain vital orbital reconnaissance photographs of Mars. But the project is put in danger when one of the astronomers is taken over by The Mysterons.