** spoiler alert ** The first thing I noticed with this novel, McEwan's second I believe, is that the reader has to guess at the holiday location. And this only after the reader manages to shift beyond the mundane activity between a holidaying couple. There are no titillating or even erotic love scenes. Sometimes it is too overwhelming to be in two characters' heads, for every minute detail to be recorded.
It is a thin novel (similar length to The Cement Garden), and the prime disappointment is the build up. The climax is disappointing. There are particular characterisations that aren't adequately explicit, raising question marks about motivations.
This is basically a story about a couple (Colin and Mary) that holidays in Venice, meets a 'stranger' named Robert, a barowner who then introduces the couple to his wife, Caroline. Robert is a sadist, while his wife is a masochist. They hatch a plan to kill Colin. Why? In the film, a reason is given, in the novel, the reasoning is bogged down by unclear dialogue (Robert's wife hinting at her masochistic nature and Robert's preference for sexual violence). In the film, Robert is arrested (I think). In the book, like most of McEwan's sobering endings, Robert and Caroline evade prosecution for the murder of Colin and Mary is left with nothing else, other than returning to England with the dead body of her lover.