"The Inquisition," the requisite "flashback" instalment of all Gerry Anderson series programmes, is an instalment of Captain Scarlet And The Mysterons, and indeed the thirty-second and last ever to be produced and/or transmitted during the programme's original run, in which a Mysteron likeness of a Spectrum Intelligence agent named Colgan tries to manipulate Captain Blue into revealing the Spectrum cipher codes, so that the Mysterons can carry out their threat that "One of the members of Spectrum will betray you all."
Paul Metcalfe and Adam Svenson have had a good meal at a restaurant called "The Markham Arms," in a location the instalment does not specify. Before they leave, Svenson is served some coffee that he has ordered. But immediately after drinking it, he feels strangely sick, and he disappears as Metcalfe is retrieving their coats.
Svenson recovers consciousness to find himself aboard what resembles Cloudbase's Control Room, with a man calling himself Colgan, and claiming to be a member of Spectrum Intelligence, demanding that he prove his identity by providing the Spectrum cipher codes.
"All you have to do is prove who you are," Colgan says.
Svenson refuses to do this, even though he does partially describe three of his and Captain Scarlet's shared experiences ("Big Ben Strikes Again!", "The Trap," and "Crater One Hundred And One") against the Mysterons.
Getting nowhere, Colgan calls his aide, who is carrying a hypodermic needle containing a truth serum. Svenson jumps out the window to discover that the setup is false, and Captain Scarlet's voice--one Svenson is glad to hear--orders him to get clear, whereupon Captain Scarlet manages to destroy the building inside which Svenson was being held prisoner, using a missile he launches from a Spectrum Pursuit Vehicle.
"Were they Mysteron agents?" Svenson asks.
"Yes," Captain Scarlet answers. Then he adds, "You can tell me all about it...back on the real Cloudbase."