This film and its sequels were a deliberately downbeat alternative to the hugely successful James Bond films, even though one of the Bond producers, Harry Saltzman, was involved with the Harry Palmer series, along with other personnel who had been contracted to work on one or more of the 007 movies.

The Plot:

A scientist called Radcliffe is kidnapped from a train and his security escort killed. Harry Palmer, a British Army sergeant with a criminal past, now working for a Ministry of Defence organisation, is summoned by his superior, Colonel Ross, and transferred to a section headed by Major Dalby.

Ross suspects that Radcliffe's disappearance is connected to the fact that sixteen other top British scientists have inexplicably left their jobs at the peak of their careers. He threatens Dalby that his group will go if Radcliffe cannot be recovered. Palmer is then introduced as a replacement for the dead security escort.

Afterwards, Dalby briefs his agents that the main suspect is Eric Grantby and his chief of staff, codenamed "Housemartin", and tells the team to find out where they are at present.

Palmer is also introduced and befriends Jock Carswell. Using a Scotland Yard contact, Palmer locates Grantby but, when Palmer tries to stop Grantby getting away, he is attacked by Housemartin.

Housemartin is arrested later but, before he can be questioned, he is killed by men impersonating Palmer and Carswell. Suspecting that Radcliffe is being held in a certain disused factory, Palmer orders a search, but nothing is found except a piece of audiotape marked "IPCRESS" that produces meaningless noise when played.

Dalby then points out that the paper on which Grantby had written a false phone number is the programme for an upcoming military band concert. There they encounter Grantby and a deal is struck for Radcliffe's return.

The exchange goes as planned but, as they are leaving, Palmer shoots a man in the shadows who turns out to be a CIA agent. Subsequently, another CIA operative threatens to kill Palmer if he discovers that the death was not a mistake.

Some days later, it becomes clear that while Radcliffe is physically unharmed, his mind has been affected and he can no longer function as a scientist.

Carswell has discovered a book titled "Induction of Psychoneuroses by Conditioned Reflex under Stress" – IPCRESS – which he believes explains what has happened to Radcliffe and the other scientists.

Carswell borrows Palmer's car to test his theory on Radcliffe, but is shot before reaching him.

Believing that he himself must have been the intended target, Palmer goes home to collect his belongings and there discovers the body of the second CIA agent.

When he returns to the office, the IPCRESS file is missing from his desk. Ross had previously asked him to microfilm the file and Palmer now believes that he is being set up.

When he informs Dalby what has happened and that he suspects Ross, Dalby tells him to leave town for a while.

On the train to Paris, Palmer is kidnapped and wakes up imprisoned in a cell in Albania.

After several days without sleep, food and warmth, Grantby reveals himself as his kidnapper. Having previously read the file, Palmer realises that they are preparing to brainwash him.

He uses pain to distract himself, but after many sessions under stress from disorientating images and loud electronic sounds, he succumbs. Grantby then instills a trigger phrase that will make Palmer follow any commands given to him.

Palmer eventually manages to escape and discovers that he is really still in London.

He phones Dalby, who is in Grantby's company at the time. Dalby uses the trigger phrase and gets Palmer to call Ross to the warehouse where he had been held. As Dalby and Ross arrive, Palmer holds them both at gunpoint.

Dalby accuses Ross of killing Carswell; Ross tells Palmer that he had been suspicious of Dalby and was investigating him.