The Mysterons: sworn enemies of Earth, possessing the ability to recreate an exact likeness of an object or person. But first, they must destroy. Leading the fight, one man fate has made indestructible. His name: Captain Scarlet.

In the year 2068, a manned mission to the planet Mars ends in disaster when the crew of an Earth exploration vehicle encounters an amazing Martian city populated by the invisible Mysterons; misinterpreting the inhabitants' use of cameras as an act of aggression, the crew believe that they are under attack and destroy the entire complex with missiles. However, the Mysteron city then recreates itself using the unearthly process known as retrometabolism, and the enraged Mysterons vow to exact their revenge upon Earth by engaging humanity in a war of nerves. The Mysterons are able convert anyone or anything to their cause by destroying the original and then recreating it as a new, ‘Mysteronised' agent - capable of employing any means necessary to bring about the downfall of the human race…
Earth's line of defence against the alien attackers is the world security organisation known as Spectrum; led by Colonel White, Spectrum uses all its available resources to thwart the Mysteron threat, including a crack team of colour-coded agents, the sleek but deadly Angel Interceptors and the tank-like Spectrum Pursuit Vehicles. One of Spectrum's top agents is Captain Scarlet; once a Mysteron agent, Scarlet was able to throw off his conditioning and regain his sense of loyalty to Spectrum, with the added bonus that he is now indestructible. Fearless in his mission to protect Earth, Captain Scarlet is aided by the brave and intelligent Captain Blue, and together they attempt to defeat the menace of the Mysterons.

Developed by Gerry Anderson, ‘Captain Scarlet and the Mysterons' is a darker, grittier series to its predecessor, ‘Thunderbirds'. The puppets used are more lifelike and correctly-proportioned, and the show has an increased level of reality and violence - characters are injured, and even die, and Spectrum are not always successful in defeating the latest Mysteron masterplan.