True crime booksReviewWhy would anyone kill a model citizen of austerity Britain? Blake Morrison investigates

It was a passing driver who spotted the woman's shoe lying by the road. Times were hard in Britain in 1946 and good shoes unaffordable; he hoped to locate the matching shoe and that the pair would fit his wife. But the other shoe, when he found it, was attached to a woman's body. She lay half-hidden in the hedgerow, with her stocking torn and her coat rucked up. He knew at once that she'd been murdered.

Many chronicles of real-life crime are also stories about places: the moor where Brady and Hindley took their victims; the Gloucester house in which Fred West buried his; the Savannah of John Berendt's Midnight in the Garden of Good and Evil. Other accounts concentrate on motive: So Brilliantly Clever, Peter Graham's study of how the New Zealand teenagers Pauline Parker and Juliet Hulme battered Pauline's mother to death (the case featured in the film Heavenly Creatures), disentangles the complex dynamic between the two girls. In Murder at Wrotham Hill, Diana Souhami's focus is different: not place or psychology but period – the when rather than the where or why. It's a story set in the early days of postwar Britain. And both the murderer and murderee were classic products of the age.

The victim, Dagmar Petrzywalski, had set out early that morning from her home – a wooden hut in Kingsdown, in rural Kent. She was in her late 40s and unmarried. For 25 years she had worked as a telephonist for the GPO. But after the London house where she'd been lodging was bombed in 1941, she suffered a nervous breakdown, took early retirement and moved to the country. Her 10ft x 7ft hut – the Vic, as she called it – had neither water nor electricity but was adjacent to the bungalow in which her widowed mother lived.

Dagmar was a model citizen of austerity Britain. She made her own clothes, grew vegetables, kept chickens, had few friends beyond her immediate family, never bothered a soul. To save money, she walked everywhere, spurning lifts from car drivers but occasionally accepting them from lorry drivers, whom she considered more trustworthy. When she left that morning with her newly acquired puppy, she planned to visit her brother and his wife in Woking. She didn't get very far.

Heading the murder investigation, Robert Fabian of Scotland Yard had little to go on at first. Dagmar had been strangled but not sexually abused (her hymen was still intact). Nor was robbery likely to have been a motive. The only lead was a yellow string bag belonging to Dagmar, which a young farm worker fished out of a lake on a private estate. The lake was several miles from where the body had been found, but it was fed by a stream that ran close to the road. More to the point, the stream passed by a cider works, to which a delivery of bricks had been made early on the morning of the murder.

Sidney Sinclair, the driver who delivered the bricks, had already been questioned by police at the thatched cottage near Cambridge where he lived with his wife, Daisy. He seemed harmless and his story hung together – until Fabian moved in on him and it unravelled. His real name was Harold Hagger; he had a long history of petty crime and small-time violence; he was also a bigamist, an army deserter and a black marketeer. The night before the murder he'd spent several hours at a café that doubled as a clearing house for stolen goods. He left with a bulging wallet. When flush like that, he was in the habit of using prostitutes.

Under pressure from Fabian, he changed his previous three statements, which denied that he had seen Dagmar walking along the road, and admitted giving her a lift. He claimed she'd offered to "play about" with him at a price (she couldn't do more because she "had the rags on") but then tried to steal his wallet. To prevent her, he grabbed the scarf she had round her neck and next thing she was dead. Sidney hoped his confession would lead to a manslaughter conviction, not murder. But to claim that a 48-year-old virgin had offered to masturbate him in return for money was never likely to impress a jury. Sidney might be manipulative and opportunistic but he wasn't all that bright.

The trial hinged on his claim that he suffered from blackouts caused by a head injury sustained many years before, when he jumped out of a moving train while under arrest. The defence presented him as a man on the verge of insanity, unaware of what he'd been doing when he killed Dagmar. But the trial lasted only two days, and the book's penultimate chapter is given over to Britain's most famous hangman, Albert Pierrepoint – which tells you all you need to know about the verdict.

Souhami tells the story plainly, without recourse to red herrings or fake suspense. As a child of the 1940s, she's fascinated, above all, by the period detail – the fact that Dagmar was strangled with a man's vest which she'd bought at the market for a shilling and wore as a scarf; that when her mother saw in the paper that a woman answering to Dagmar's description had been found murdered, she had to trek to the telephone box to inform the police (hers wasn't one of the 4m British homes with a phone); that Pierrepoint hanged 253 men in the three years after the war, all but 27 of them Nazi war criminals. Coal shortages, ration-books, thrift, making do, pulling together, the return of bananas – they're all there. At best this use of zeitgeisty minutiae is enriching, at worst distracting. Too often Souhami tells us things we know already or which add little or nothing to the tale.

In her acknowledgments, she admits that she "dithered" over choosing the subject of her book, and was also tempted by the case of Margaret Allen, who dressed as a man, worked as a bus conductor, and hammered an elderly neighbour to death in 1948. Souhami went for Harold aka Sidney because more source material was available and she was able to interview relatives of those involved. Perhaps the choice was a wrong one, nevertheless. All murders are interesting but some are more interesting than others. Why spivvy Sidney was worth resurrecting isn't entirely clear.

Blake Morrison's The Last Weekend is published by Vintage.

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