Four further episodes chronicling Captain Scarlet's battle to save Earth from a Mysteron invasion. 'Spectrum Strikes Back' concerns the unveiling of some new weapons designed to protect Earth against Mysteron aggression. 'Special Assignment' finds Captain Scarlet involved in some apparently underhand activity with his nemesis Captain Black. 'The Heart of New York' has Spectrum investigate a potential Mysteron attack on the Big Apple. And 'Lunarville 7' finds Scarlet perplexed when a human moon colony forms an alliance with the Mysterons.