Set in 2068, the series depicts a "" between Earth and the Mysterons: a race of Martians with the power to create functioning copies of destroyed people or objects and use them to carry out acts of aggression against humanity. Earth is defended by a military organisation called Spectrum, whose top agent, Captain Scarlet, was killed by the Mysterons and replaced by a reconstruction that subsequently broke free of their control. Scarlet's double has a self-healing power that enables him to recover from injuries that would be fatal to anyone else, making him Spectrum's best asset in its fight against the Mysterons.