Deep in plot factors and to some perhaps slow in development (but layered spy films need to "develop" to set the story in play). But steeped in cold war motivations and sensibilities of the time. Peppard is driven to do his job well, with concern for protecting those things and people he values. Twists and turns confront him, but he resolves the factors. But then there is that final and jaw-dropping question which is the final line of the film!
His former controller offers him a position of command within the British espionage structure from which George Peppard has left. Disgusted with the way in which the prior situation was handled (set up by his overseers) Peppard might be presumed to say NO, but my presumption is that the answer would have been YES.
Watch the film and screw your head on tight, no exits to bathroom without pause button pushed, this is not a trivial action film.