The protagonist is assigned as a lookout and kills the occupants of a car which suddenly arrives on the scene, believing them to be operatives working for Jay; they instead turn out to be members of the US Office of Naval Intelligence.

The protagonist takes refuge with Charlie Cavendish, the father of a friend killed during the Second World War, and attempts to re-establish contact with WOOC(P) without being arrested.

The protagonist escapes, but is captured and taken to meet Jay—he has, however, allowed military intelligence to follow them, and Jay and Dalby are arrested by Colonel Ross.

The protagonist reveals to Jean that Jay and Dalby were using a process called "Induction of Psycho-neuroses by Conditioned REflex with StresS" (IPCRESS) to brainwash the VIPs into loyalty to the Soviet Union.

The links that Carswell had discovered were in fact indicators of the personality traits that Jay had used to determine which VIPs would easily succumb to the process.

The novel ends with the protagonist concluding his report to the Minister, revealing that Jay has turned and begun working for the British, while Dalby has ostensibly died in a car accident.

[1] In 1992 he said that the inspiration to write the novel came from his real-life neighbour Anna Wolkoff, a White Russian émigrée who collaborated with a cipher clerk from the American embassy to spy for Germany in World War II.

Deighton's mother cooked for Wolkoff's dinner parties and he said that he "vividly" remembered when MI5 officers came to arrest her: "The experience was a major factor in my decision to write a spy story at my first attempt at fiction.

"[2] The plot involves mind control, the acronym IPCRESS of the title standing for "Induction of Psycho-neuroses by Conditioned Reflex under Stress".

The brainwashing is similar to a shock technique called psychic driving pioneered by Donald Ewen Cameron in the 1950s, originally on unwitting mental hospital patients, which was used and funded by the Central Intelligence Agency's secret MKULTRA program in Canada.

Early in the novel we learn that he worked for Military Intelligence for three years before joining his present agency – WOOC(P) – as a civilian employee.

The film medium made it difficult to maintain the anonymity of Deighton's hero, who acquired the name Harry Palmer.