A Mysteron spacecraft enters Earth atmosphere and is engaged by the Angel fighter craft. The Mysteron craft avoids destruction and goes on to land in northern Australia. Scarlet and Blue go to investigate.
The designer of the devastating Thunder Pulse compression bomb is presumed killed and replaced by the Mysterons. Spectrum turn to his twin brother who is a convicted criminal in the hope he can make some sort of mental link and stop whatever plan the Mysterons are trying to execute.
The Mysterons attempt the takeover of a new advance warship the 'Proteus' Their attempt is only partially successful and a running battle evolves between the ships automatic systems and Spectrum agents trapped on board.
Scarlet and Blue track a stolen Russian tank into the Alaskan wilderness. There they find a whole town overtaken by the Mysterons. Their mission this time is to unleash one of the greatest terrors in the galaxy on the human population of Earth.