When Joe Pearce is knocked off his bike in rural Sussex in a hit-and-run accident and subsequently dies from a head injury, Jim Manning suspects that the driver of the car that struck the man a glancing blow was the amoral, essentially pleasure-seeking (“I just want to be happy, and on the whole I prefer other people to be happy too”) local aristocrat Bill Bule, a friend of his and his wife Jill. His hunch proves to be almost correct: it was Bule’s car that hit Joe but, crucially, Jill reveals not just that she was driving at the time but also that she has been having an affair with Bule. Unaware that she had hit the cyclist, Jill had not stopped the car. Despite Jim being a morally upstanding—not to say priggish—individual, he does not want his wife to go to jail and so the Mannings and Bule agree to keep their mouths shut.
P. C. Eddie Cator, the brother of Joe’s widow, Elsie, begins to investigate the case. In the meantime, Jim and Jill take a short holiday in Paris. Jill and Bule then holiday in Spain while Jim goes to Venice with some American friends before the three principals meet up again in Paris. After all this European travel Jill admits to being in love with Bule. Although she also wishes to remain married to Jim, he feels differently about the matter. Piqued, he responds by putting their house on the market and the couple begin living apart.
Eddie hones in on Bule as the prime suspect for Joe’s manslaughter, aided by an anonymous poison pen letter that Jim instantly realizes must have been written by Bule’s recently sacked chauffeur Lee:
‘Have you found out where the “Honourable Bule” was half-past six when Joe Pearce was killed if he says he was home it’s a lie he wasn’t but somewheres else…’
Jim therefore deploys a prefabricated alibi, hoping that his standing as a magistrate will elevate him above suspicion in the eyes of the police. Having sold his house and moved to London, Jim then enjoys a brief fling with a woman called Philippa who helps him through a difficult patch whilst Jill is living with Bule.
One evening Bule tells Jim that he has argued with his lover and that she has walked out in a huff. Bule’s repetition of the form of words used by Jill during the argument—“I wanted to, and you wouldn’t let me, and now it’ll never come right”—leads Jim to suspect that she has gone to Sussex to confess to Elsie that she was responsible for Joe’s death. In dramatic fashion, Jim and Bule drive at high speed from the centre of London to Sussex, hoping to reach Elsie’s cottage before Jill, whom they assume is travelling down by train, has had time to spill the beans. Although the two men arrive in the nick of time, Jill then breaks down and confesses that she was driving the car that killed Joe. Elsie decides to keep this knowledge to herself so as to protect Jill from any retribution from Eddie and then remains staunch in the face of a verbal onslaught from the policeman, who thus fails to discover the identity of his brother-in-law’s assailant. As part of the fallout from the evening, Jill returns to Jim and they resume living together.
About a month later, quite by chance, Jim finds out that Bule is very ill with TB. He visits him in hospital, whereupon the invalid tells him to keep mum: “Don’t go home and tell madam all about this”. Jim promises to comply with Bule’s request but then promptly goes and does precisely the opposite, considering that not to tell Jill would be too caddish, too Bule-like. When she hears the news, Jill rushes to Bule’s bedside and ends up travelling with him to Switzerland, where he makes a significant recovery.