After a landing on Mars by a Spectrum exploration vehicle, Earth is under attack from the Mysterons.

As Captain Scarlet and the other Spectrum agents prepare to defend the Earth against this terrible threat, they know that anything could happen. For the Mysterons have powers beyond the understanding of man — and they are determined to destroy all life on Earth! Captain Black becomes the Mysterons' pawn, and Captain Scarlet take on a vital job, escorting the World President on a dangerous journey. But can Scarlet resist the deadly power of the mysterons?