Set in 2068, the series depicts a "war of nerves" between Earth and the Mysterons: a hostile 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 murdered by the Mysterons and replaced by a reconstruction that later broke free of their control.
The Mysterons reconstruct the driver, the transporter and the reactor to carry out their latest threat: to bring devastation to the Atlantic Seaboard of North America and thus "deal a heavy blow to the prestige of the world".
[1] The miniature models of the transporter truck and nuclear reactor were originally built for "Big Ben Strikes Again", in which the Mysterons hi-jack an atomic device in an attempt to obliterate London.
[1] One of the deleted scenes shows Scarlet and Blue obtaining their SPV (stated to be number 442) from a village shop whose owner is shown dressed in nightclothes and a baseball cap.
[1] The script also clarified the Mysterons' objectives, with Colonel White (voiced by Donald Gray) realising that the aliens intend to crash the reactor into the Expo 2068 site, triggering a nuclear explosion.
Though unimpressed by the miniature model of the Seneca helicopter's cargo container, he remarks that the scene of Scarlet sawing his way inside "reveals an amazing level of concentration, skill and dexterity behind the camera.
"[10] Writer Fred McNamara praises the climax, calling it "one of the most satisfying action set pieces" of the series and commenting that the scenes of Scarlet inside the container demonstrate some "tricky marionette manoeuvring" and "exquisite model work".