The Man from X, originally transmitted on ITV, 18 May 1969
Directed by Gil Taylor, written by Tony Williamson

London, February 2nd. A young couple witness a man in a spacesuit stumble from a building and die. At the United Nations in New York, Curtis Suretse informs Stewart Sullivan that the man had been operating in a sub-zero vacuum inside the building when his air supply had run out and his helmet jammed. In an attempt to identify where the spacesuit originated, Stewart visits an aerospace institute in Farnborough that is working on a space research project. Despite assurances from manager Carter that all of their ten spacesuits are accounted for, Stewart's snooping reveals that five have been replaced by frogmen suits. Meanwhile, a tamperer has fitted his car with a canister of liquid oxygen. While driving away, Stewart becomes delirious from the extra oxygen but is able to throw himself from the car before it explodes.

From the traces of nitro-glycerine under the corpse's fingernails, Jason King establishes a criminal connection and identifies the body as safecracker James Rankin. Jason is rebuffed by Rankin's sister Leila at a discotheque, but when he rescues her from some heavies, she gratefully accepts refuge at his apartment. Leila informs Jason that her brother had been preparing for a major robbery that involved cracking a safe with a magnetic combination. Jason surmises that another safecracker must be arriving from America, where such safes are in use. He manages to apprehend the replacement, Max Rinston, when he arrives at London Airport from New York.

Masquerading as Rinston, Jason is picked up at the airport by gang members. When they realise they are being followed by Annabelle Hurst, they set a trap for her, and Jason must pretend to shoot her in order to maintain his cover. With the aid of Interpol's computer in Paris, Annabelle and Stewart deduce that the location of the safe to be cracked borders onto the sub-zero vacuum of a frozen food factory. Meanwhile, Jason learns from Carter, who is masterminding the raid, that two million pounds worth of diamonds are to be stolen. Donning their spacesuits, the gang enter the vacuum, where Stewart is concealed in the spacesuit recovered from Rankin. Together, Stewart and Jason overcome the gang and foil the raid. Before withdrawing with Leila, Jason reveals that he could have cracked the safe easily, having learnt all the relevant combinations.