Dateline - the day after tomorrow. When a mysterious extraplanetary signal is detected emanating from Mars, the world security organisation known as Spectrum sends agents Captain Scarlet and Captain Black to investigate. Reaching the red planet, the two men leave their ship and head for the surface in their Bison Alien Terrain Vehicle, where they soon discover the source of the signals; a huge alien city, which materialises before them. The aliens dispatch a probe to examine the Earth vehicle, but Black assumes it to be hostile, and fires a burst of missiles which destroys the entire city. However, the alien buildings immediately reform, and the citys inhabitants, the Mysterons, retaliate by killing Black and declaring war on Earth. Scarlet manages to return to Earth with Blacks body, which receives a hero's burial; the ceremony is a sombre one, attended by Blacks colleagues and his bereaved girlfriend, Destiny Angel. Later, the head of Spectrum, Colonel White, calls a meeting to discuss the Mysteron threat. But the aliens then take over Captain Scarlet to act as their instrument of destruction - and Scarlets first act is to disable the engines that keep Spectrums mighty Skybase aloft...
- Wayne Forester (Captain Scarlet)
- Robbie Stevens (Captain Blue / Skybase Engineer / Skybase Medic)
- Emma Tate (Destiny Angel)
- Mike Hayley (Colonel White / Voice of the Mysterons / Narrator)
- Jules De Jongh (Lieutenant Green / Shuttle Computer / Skybase Control)
- Nigel Plaskitt (Captain Black / Doctor Gold / Hank McGill)