When the Mysterons threaten to destroy key links in the Frost Line Outer Space Defence System, Captain Scarlet and Lieutenant Green race to investigate the mysterious deaths of the personnel at Red Deer Base.

A truck carrying an atomic core reactor to the new Manicougan power complex falls into the hands of the Mysterons who intend to use it to strike the Atlantic Seaboard of North America.

Captain Scarlet and the rest of Spectrum are in a desperate race against time to defeat the Mysteron's latest threat, the total destruction of the massive desalination plant at Najama, high in the Andes Mountains.