A World Air Force plane carrying Commodore Goddard and his right-hand man, being escorted by Melody Angel, is struck by lightning, and crashes, soon being reconstructed by the Mysterons.
The force broadcasts its current threat: that they aim to kill all 10 of the world's top air-chiefs, who make up the executive Supreme Command of the World Air Force, who want to discuss a plan to dissolve the war of nerves between Earth and the hostile force. They plan on doing so by holding an International Air Conference at the loneliest location in Europe; Glen Garry Castle in Scotland.
This is however unknown to Colonel White, who is awaiting the approval from Captain Scarlet that the castle's security is set up and approved. After she brings the delegates to the castle to start the conference, Symphony Angel is taken prisoner, as is Captain Scarlet, who unexpectedly discovers the brutal plan before the delegates arrive.
Leaving the air-chiefs with no warning, and in perfect firing positions to be massacred by Goddard and his personal cohort aid, will Colonel White realise in time that something is wrong? Can Captain SCarlet save the day?