Set in 2068, the series depicts a "" between Earth and the Mysterons: a hostile race of Martians with the ability to create functioning copies of destroyed people or objects and use these reconstructions to carry out specific acts of aggression against humanity. Earth is defended by a military organisation called Spectrum, whose top agent, Captain Scarlet, was murdered by the Mysterons and replaced with a reconstruction that later broke free of their control. The double of Scarlet has powers of self-repair that enable him to recover from injuries that would be fatal to any other person, which make him Spectrum's greatest asset in its fight against the Mysterons.