Novelist Maurice Bendrix (Ralph Fiennes) narrates the film, which is about the affair he has had with a beautiful woman, Sarah Miles (Julianne Moore), who is married to a senior civil servant, Henry Miles (Stephen Rea). Sarah has never been particularly happy with Henry, who is intelligent but dull, and tends to focus exclusively on his work for the government.
The movie is very well crafted, re-creating the sepia and foggy atmosphere of London in the 1930s and 1940s very well, including the war years, with the toll that the Blitz takes on the city and its inhabitants. In this respect, it is very much a period film. Essentially, this is a sentimental drama focused on Maurice and Sarah, who engage in a passionate affair as they fall madly in love. But the conventional triangle - lover, mistress and husband - is not all there is to the story: the 4th party to the story is God, as Sarah's Catholic faith very much is part of the equation. Representing God, so to speak, is a Catholic priest, Father Richard Smythe (Jason Isaacs).
One recognises themes that recur in the novels of Graham Greene (the film is based on the novel of the same title), for whom faith and Catholicism were central concerns: coming to terms with one's sins (if one is prepared to recognise them as such), seeking redemption for them (or not), and so on. In the last analysis, the even deeper question is asked: does any of that matter if God does not exist, and how do we know that He does exist, and that He cares?
So, what could have been a mere sentimental drama set in the past becomes, in the process, something more complex and more profound - an unusual storyline in some respects, with a dark, metaphysical side. The film is intelligent, captivating and interesting in many respects, but it is also rather gloomy, in a way that you cannot shake off, as if it stuck to the skin.