Investigating reports of a Mysteron cell operating in Phoenix, Arizona, Scarlet trails a pair of Mysteron agents to a remote desert diner. There he overhears the agents bribing Spectrum flight-engineer Xander Story to smuggle a bomb aboard Skybase, but when he attempts to apprehend them, Scarlet is shot down. Then the Mysterons drive a petro-chemical truck into the diner and Scarlet is incinerated in the explosion. Blue finds Scarlet's body and returns it to Skybase, but Scarlet's injuries are too severe even for the retrometabolisation process and he is pronounced dead. However, Scarlet recovers consciousness to find himself apparently alive and well - until he realises that he has become intangible and none of his colleagues can see or hear him.

• Gerry Anderson

• Emma Tate
• Mike Hayley
• Wayne Forester