Imaginative and fantastical Supermarionation fun in the year 2065 when Earth's security organisation, Spectrum, spearheads an expedition to Mars. The local inhabitants, the Mysterons, mistakenly believe the arrival of the earthlings signals attack. Captains Scarlet and Black are captured and given the power to recreate themselves, even after being killed. Scarlet escapes, maintaining loyalty to Spectrum, while Captain Black becomes the Mysterons' pawn. Spectrum battles the deadly forces of the Mysterons.