Of the dozen or so Graham Greene books I've read, Our Man In Havana (1958) is the most humorous and sardonic. Wormold, a vacuum cleaner salesman in Cuba when Batista was president, is approached by an MI6 agent who wants him to gather intelligence. Wormold takes this side job because he needs the dough; it costs him a lot to satisfy his sixteen-year-old daughter. More than that, he enlists several spies of his own who are actually fictions he's created so he can pocket the wages and expenses intended for them. To spice up his reports for MI6 and to keep the money flowing, he takes a bunch of close-up photos of vacuum cleaner components and tells MI6 they're aerial shots of a secret missile installation in the hills (note that the book came out four years before the Cuban Missile Crisis). This ramps up the action and puts Wormold and his friends and associates, and a dog, at risk of elimination, maybe by the Russians.
For anyone who hasn't read Greene before, this might be the best of his novels to start off with, as it's quite entertaining and accessible from start to finish, whereas his other books can be complicated and dive deep.
Also, Greene was a master at creating unique narrative voices and styles across his works, and as I felt with some of his other books, Our Man In Havana seemed to me as if it was written by a different author or, perhaps more accurately, by a different version of Greene himself (compared to, say, the very different voices and styles in Journey Without Maps (1936), A Gun for Sale (1936), and The Heart of the Matter (1948)).