This adaptation of Len Deighton's novel was produced by Harry Saltzman who, up until 1974, also co-produced the Bond movies with Albert R. Broccoli. However, it's practically the polar opposite to 007 in terms of approach, eschewing the exaggerated escapist fantasy trappings in favour of a far more muted, realistic style.
The visual language is one of off-kilter claustrophobic camera angles and sombre colour grading. Most of the runtime focuses on endless legwork and slow-burning tension, interrupted with only a few short bursts of violent action. Michael Caine comes across like an ordinary bachelor who would just as easily spend his time cooking up fancy dishes in his kitchen as he would trailing a suspect.
It's a well-acted, impeccably-crafted thriller where the intrigue unfolds gradually via small, fascinating details. The most memorable part, however, is the gruelling brainwashing sequence that leads to a suspenseful dilemma of a finale.