Spectrum officer Captain Black attacks an alien city on Mars, invoking the wrath of its ethereal inhabitants: The Mysterons. Their first act of vengeance is the attempted assassination of the World President. As part of their scheme, The Mysterons kill Captain Scarlet. They reconstruct him, now invincible and under their control but otherwise indistinguishable from the real Captain Scarlet. Will Spectrum detect the imposter in time? Will fate free the un-killable Scarlet from the Mysteron influence, making him a powerful asset for humanity in this "war of nerves"?

Spectrum and the World President attend a secret conference on an African game reserve to demonstrate two new anti-Mysteron gadgets, a Mysteron Detector and a Mysteron Gun but the aliens announce they intend to sabotage the event.