Captain Black and Captain Scarlet are sent to mars to investigate a mysterious alien signal coming from there. A misunderstanding occurs and the Mysterons vow revenge. They are killed and both become Mysteron agents. Back on earth Captain Scarlet tries to destroy skybase, but he fails, so Captain Black is revived to do the Mysterons bidding.

Captain Black is linked to a blast at a military research installation; Scarlet and Blue liaise with the FBI in a bid to trace the rogue Spectrum agent.

The Angels shoot down a USAF transport plane that was heading for Skybase, but it releases a swarm of cyberbugs, advanced robots the size of a bug that are capable of eating metal and reproducing with great speed. Once they are aboard Skybase, they set about eating their way towards the atomic reactor core. The headquarters will be destroyed unless Scarlet can find a weakness.

Three weeks after losing contact with Elysium Base on Mars, a team consisting of Captains Scarlet and Blue, Destiny and Harmony Angels, and Doctor Gold are sent to find out what happened to the crew. On arrival, they realise it is a Mysteron trap and that they are under attack from an titanium armour-plated research robot named Remote Acquisition Technology (RAT) which carries lasers and a diamond-tipped saw. Under Mysteron control, the RAT has become the ultimate killing machine.

An escape pod from the first manned mission to Jupiter crash-lands in the Arctic. The one surviving crew member is Lt Green's father. But is the survivor all he seems?

Destiny and Blue lose control of Mercury, a nuclear-powered shuttle; Spectrum then receives a ransom demand with a threat to crash-land the shuttle on Washington DC.