A divulged, top-secret meeting with the World President and two Spectrum Intelligence Agency officers, one of which is a general, the other a science doctor, who has created a new Mysteron electrical gun & detector following the inexplicable events with the late Doctor Magnus who attempted to kill General Tiempo, takes place in the shooting grounds of an African private game reserve. Colonel White and Captains Scarlet and Blue find themselves in a treacherous hunting sport, when the Mysterons helplessly attempt to prevent Spectrum from conducting the usage of their two brand new and innovative mobile weapons where one can kill a Mysteronised person with a strong electricity voltage, the other can distinguish and identify Mysteron characteristics within a person using normal X-Ray systems. But, unbeknown to the group of men, there security officer-in-charge, Captain Indigo, has been murdered in cold-blood by Captain Black.