Four episodes chronicling Captain Scarlet's battle to save Earth from a Mysteron invasion. In 'The Mysterons' Captain Black becomes the victim of Mysteron mind control and Captain Scarlet submits to an operation which makes him indestructible. 'Winged Assassin' has the Mysterons capture a plane carrying the Director General of the United Asian Republic. 'Big Ben Strikes Again' sees Spectrum go into action when a nuclear transporter disappears in London. And 'Manhunt' has Captain Black both infiltrate the Culver Atomic Centre and kidnap Symphony Angel.