The Mysterons threaten to kill Colonel White and after their initial attempt fails, White elects to leave Cloudbase so as not to place the other Spectrum agents in jeopardy.

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.

When the Lunar Controller claims he can negotiate peace between the moon and the Mysterons, Captain Scarlet, Captain Blue and Lieutenant Green are sent to the moon to investigate.

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

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.

When the Mysterons threaten to sabotage a vital conference at Lake Toma in Switzerland, Scarlet and Blue are assigned to escort the world's leading astrophysicist, Dr. Conrad, to Geneva.