Graham Greene, with his unfaltering sense of reality and irony, plays no favorites in the world of espionage. He knew (as Eric Ambler did, and as John Le Carre did) that no country is really an innocent - that all countries have guilty secrets that other countries (for purposes of self-interest, including security and economic strength) have to discover. Keeping this in mind one easily has the situation in OUR MAN IN HAVANA.
Alec Guinness is Wormold, an Englishman who runs a vacuum cleaner agency in Havana, Cuba in the late 1950s (actually before Castro seized power). He lives with his daughter Jo Morrow, who has some spending habits of her own. He does not make much money, and is in debt. He is approached by British Secret Service official Noel Coward to become a British agent, reporting on Cuban military information for a monthly stipend. Guinness agrees reluctantly because of his debts, but he really does not know how to develop a spy ring. Coward gives him some vague tips that he takes up, but he fumbles them. He attempts to approach some local Cubans he knows from his social club, and they think he is trying to come onto them.
Soon he is joined by Maureen O'Hara, who is to be his "bookkeeper"/assistant, but was sent by Coward and his boss Ralph Richardson. Struggling to make something to report about his activities, Guinness starts lying. He makes it sound like he was successful getting those Cuban gentlemen to be his information gatherers. But worse, he decides he has to prove he found something. He notices that the vacuum cleaners, if taken apart and blown up a huge number of times, they look like odd buildings for scientific or military purposes. He sends these to England, and Richardson is deeply impressed, although he does comment that one would think they look like parts of a vacuum cleaner. Coward happens to hear this while he is behind Richardson, and suddenly realizes what Guinness is sending. But he keeps quiet.
There are people who are suspicious of Guinness. O'Hara catches on early, but she has fallen in love with Guinness and is keeping (despite misgivings) quiet. But the local police chief (Ernie Kovacs) is aware - after hearing of the approaches Guinness was making to those local fellows, that Guinness was recruiting spies. However, Kovacs (for his own reasons) is mum about this - he is interested in getting Guinness's agreement for him to marry Morrow (who doesn't like him). Guinness's closest friend, a former German army officer played by Burl Ives, also figures out what is going on, and willingly sells his information (or a variant of it) the the Russians.
Soon Guinness finds his seemingly harmless fraud is actually dangerous. Coward comes to see him to warn him that the Russians are so impressed at Guinness's "successful" discovery of military secrets that they have decided to silence him by assassination, most likely poisoning at a public dinner Guinness has to attend of vacuum cleaner salesmen. Guinness manages to figure out who the threatening Russian agent is, but he is unable to prevent one murder. In seeking to avenge it, Guinness has to allow Kovacs to outwit himself in a checker game (you'll see what I mean).
Guinness, according to the biography by Piers Paul Read, was not happy about his performance in OUR MAN IN HAVANA. He and director Sir Carol Reed (THE THIRD MAN's director) disagreed on how Guinness should play Wormold (his character), and Sir Alec said he lost interest in it. He also did not feel comfortable with Kovacs and Ives. Noel Coward, in his diaries, did not like Ives, who he said was a bore. But still the performances are highly watchable (in Coward's case it is one of his best film roles), and the Greenean irony stays on until the end of the film. It is a clever movie, and well worth watching.