In 1968, an East-West agreement is established to jeweller протокол nuclear proliferation. One of its clauses, the Fourth Protocol, forbids the non-conventional delivery of a nuclear weapon to a target. New Year’s Eve and finds a number of top secret NATO files that should not have been there. In Glasgow, a Soviet sailor is struck by a truck while fleeing from a port guard.

Among the dead man’s possessions, Preston finds a disk of polonium, which could only be useful as a component of a detonator for a bomb. He informs Harcourt-Smith, but is promptly suspended, as Harcourt-Smith believes that Preston is manufacturing a fake incident to work his way back into MI5. Under her guidance, they assemble the device from seemingly harmless items and she sets it on a two-hour delay per their instructions. Unbeknownst to Petrofsky, Vassilievna follows her own orders, resetting the delay to zero. Afterwards, Petrofsky is observed contacting Winkler. Preston tracks him to Ipswich, loses him, then finds him again. Preston eventually realises that Petrofsky’s target is RAF Baywaters, and locates Petrofsky’s house, which lies right next to the base.

When Petrofsky starts to activate the bomb, on an impulse, he checks the timer first and realises he has been betrayed. At that moment, an SAS team storms the house and during a struggle, Preston subdues and disables Petrofsky. To Preston’s outrage, one of the SAS team cold-bloodedly executes Petrofsky, explaining afterwards that he had orders to do so. At Hemmings’ funeral, Preston is unsurprised to find Irvine secretly meeting with General Karpov.

Preston had become suspicious when known KGB agent Winkler was used as a courier, making it easy to follow him, and also when Petrofsky was killed instead of being captured for questioning. He surmised that discrediting Govorshin would benefit both Irvine and Karpov. Preston does not see any point in exposing them and leaves after expressing his contempt for their cynical power play. Michael Caine read the draft manuscript of the novel and suggested to Forsyth that they produce a film together.

They hired George Axelrod to write a script and John Frankenheimer to direct, but were unable to raise finance. Axelrod and Frankenheimer left the project, Forsyth wrote the script himself and they got a new producer and director. Much of the film was shot in the Heelands district of Milton Keynes, the main house featured is on Tranland Brigg, Heelands, Milton Keynes. The film opens with the killing of Kim Philby, who has already planned the operation, because he knows too much. In the book, he remains a key figure. The film begins with Preston breaking into Berenson’s house to expose him as a traitor.