Juan Pujol-Garcia, codenamed Garbo, was a Lisbon-based double agent during the Second World War. He convinced the Germans he was running a network of British-based agents when in fact he was inventing all of the intelligence from maps and reference works. Graham Greene, who worked for British counter intelligence in Portugal for a time during the war, reporting to Kim Philby (himself a double agent for the Russians), took the Garbo story as inspiration for the character of James Wormold in Our Man in Havana.
The result is an almost perfect novel. Wormold is a vacuum cleaner salesman, recruited into British intelligence by a spy named Hawthorne. Unable to stomach a life of espionage but desperate for money to pay for his teenage daughter's extravagant lifestyle, Wormold resorts to making up his agents and their reports.
His fabrications are too successful and Wormold creates ever more elaborate lies to sustain his 'career'. Those lies too backfire and he is forced into more lies and so on. It's a wonderfully funny satire of the spy game and, more generally, of patriotism.
The great strength of the plot is its believability. The story is faintly ridiculous but Greene keeps it just plausible enough to carry you along. Each character has a good reason - vanity, for example, or stupidity - for not seeing through the deception.
Greene's characters are well-drawn and complex and he evokes the sense of place brilliantly. He has a knack for writing about rumpled Englishmen in hot climates if this and The Heart of the Matter, the only other Greene novel I've read, are anything to go by.
It's a joy from beginning to end.