Graham Greene once said that he had to read aloud, because he found himself unable to read by the eye. No doubt his thoughts were screaming vociferous theological debates at each other too loudly for the man to concentrate. Many people find a clash between their religion and behaviour; few are so obsessed with the problem that they write about it as prolifically as he did.

"The End of the Affair", one of Greene's least well-known but most intensely personal novels, inspired by his own real-life dalliance with an American lady named Catherine Walston, is about how a pact with God brings misery to two of its characters by supplying them with a reason to end their adulterous love affair. The desires of their flesh are strong, but the partner who made the pact is too afraid to break it, and the other one becomes too frustrated to continue being loveable.

The man is Maurice Bendrix, a young novelist whose reputation is steadily growing, played in Neil Jordan's film adaptation by Ralph Fiennes. His lover is his neighbour Sarah Miles (Julianne Moore), the wife of civil servant Henry (Stephen Rea), an ineffectual chap who has never been much interested in engaging his bride in physical passion. Maurice and Sarah meet at a cocktail party thrown by Henry for his colleagues, and become drawn to each other mainly out of need -- the film is set in London during World War II, and neither of these people have companions for the cold, the silences or the air raids.

It is one of these raids which disturbs the course of their relationship. Maurice seems to have been crushed by rubble; Sarah panics, pleads with God to save his life, and says that if her wish is granted she will put an end to their seedy liaisons. Maurice turns out to be alive, and Sarah breaks contact with him.

The book, narrated by the Maurice character as a bitter "journal of hate", was quintessential Greene because it didn't have a clear idea of who God was, or if He even existed, but still threw strong anger at Him. And it was a fascinatingly tragic and pathetic drama because Maurice was using God as an excuse for the demise of something that could never have lasted. Affairs always deceive someone who won't stand to be deceived, and hence are doomed. Maurice refuses to face this, and lays the blame on friends, family, onlookers, Henry, Sarah and the Almighty.

The film's first hour is very good, capturing this tone of a poet slinging back whiskies as he tells a barman how sickening it is that the good times are over. Fiennes's face is unmoving, constricted, sour and angry. The surroundings are damp, ominous and dark; cold, lifeless streets plagued by rain act as the visual accompaniment to the harsh voice-over.

Such technical proficiency continues throughout, but at some point in its second half, Jordan's screenplay suddenly turns into a depressingly conventional story of forbidden love. Sarah decides she can't keep her promise to God, and her and Maurice reunite! When they are finally separated by her death, the movie's conclusion is the same as the novel's -- Maurice protesting against the merciless nature of God -- but his reasons are a lot less interesting. Sarah's promise is, quite rightly, the cornerstone of Greene's story, but it's rather irrelevant under Jordan. He just sees it as a handy plot device to cause the lovers' initial break-up.