After a misunderstanding on the planet Mars, a war is started between humans and an alien race called The Mysterons. Thier first act of revenge is to try and assassinate The World President.
When the Lunar Controller announces the Moon's independence from Earth in the war of nerves with the Mysterons, Scarlet, Blue and Green journey to Lunarville 7 to investigate reports of an unauthorised complex under construction in the Humboldt Sea.
The Mysterons second target is the Director General of the United Asian Republic. The Director is on a visit to London and is scheduled to fly back to Asia via London airport but the Mysterons have other plans.
When the Mysterons threaten to destroy key links in the Frost Line Outer Space Defence System, Scarlet and Green investigate the mysterious deaths of the personnel at Red Deer Base.
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.
Scarlet, Blue and Green volunteer for a dangerous mission to remove the power source of the Mysteron complex in Crater 101 before it is destroyed by a low yield atomic device.
Mysteron agent Judith Chapman steals a phial of deadly K14 virus - enough to kill ten million people - from Biological Research Station D near Manchester.