Irene Violet Munro was a typist for a firm of chartered accountants in Oxford Street, London. In August 1920, when her widowed mother Flora travelled to visit family in Portobello, Edinburgh, Irene chose instead to take a fortnight by herself in Eastbourne - the kind of small independence a seventeen-year-old earns and her mother, after some discussion, agreed to. She booked lodgings at 393 Seaside, paid her landlady Ada Wynniatt the weekly rent of 30 shillings in advance, and on 16 August travelled down from London. The first days she wrote home cheerful letters. She visited Beachy Head. She walked the front. By 18 August, Mrs Wynniatt noticed her young Scottish-accented lodger had grown quiet. 'My mother wanted me to go to Scotland with her,' Irene told her. 'I should have gone. I wish I had gone now.' The next day, 19 August, she met two local men. They walked her toward the Crumbles.

Field was nineteen. Gray was twenty-nine, married, ex-army. The full circumstances of what happened on the shingle that afternoon were established only at the trial, which took place at Lewes Assizes before Mr Justice Avory in December 1920. Eyewitnesses had seen the three of them walking arm-in-arm toward an isolated section of the beach at about four o'clock; nobody saw Irene again until her body was found two days later, half-buried in the pebbles, her skull crushed by what investigators concluded was a bludgeon. Her bag was missing. Field and Gray were arrested. Their accounts contradicted each other. They were both convicted of murder and both hanged at Wandsworth Prison early in 1921. The motive, when the court reconstructed it, was robbery: two men assumed a girl on holiday must be carrying enough money to be worth killing for. She was not. Irene was a working girl, and her two-week holiday represented most of what she had saved. Her mother attended the trial and then went home to South Kensington.

Four years later, in April 1924, a different woman travelled down to the same coast. Emily Beilby Kaye was a 38-year-old shorthand-typist working in the City of London. She believed she was about to start a new life abroad with her lover Patrick Mahon, a married thirty-three-year-old sales manager who had told her he was free to leave his wife. He was not free. Mahon had a long history of theft and one previous conviction for the attempted murder of a domestic servant during a 1916 burglary, an attack so violent the trial judge concluded only the woman's thick hair had saved her life. Emily, who knew none of this, was pregnant. Mahon rented a small bungalow at the eastern end of the Crumbles - locally called the Officer's House - and brought her down for what he told her would be the start of their elopement. He brought, separately, a butcher's knife and a small saw. He had decided what he was going to do before they arrived.

When the case unravelled - through a left-luggage ticket at Waterloo Station that Mahon's wife found in his coat pocket and a Scotland Yard detective tracked to a Gladstone bag containing bloodied women's clothing - Mahon at first denied everything. After hours of questioning he fell silent, stared at the floor for nearly fifteen minutes, and then said: 'I suppose you know everything. I'll tell you the truth.' He confessed to killing Emily Kaye at the bungalow on the Crumbles around 16 April 1924. He claimed her death was accidental, the result of a fall during a struggle. He had then dismembered her body over the following days, attempting to burn parts of it on the bungalow's fire and dispose of others by throwing them from train windows on journeys to and from London. The crime, and the methodical horror of the cover-up, made him notorious. Mahon was tried at Lewes Assizes, like Field and Gray, before Mr Justice Avory. He too was convicted, and hanged at Wandsworth Prison on 9 September 1924. Emily Kaye, who had believed she was at the start of a new life, was buried by her family. Her name, like Irene's, deserves to be remembered for itself rather than for the geography of where she died.

The Crumbles, as a named stretch of coast, has largely been built over. The Sovereign Harbour development - opened in stages from the 1990s onwards - converted much of the old shingle into a yacht marina with restaurants and seafront housing. The Officer's House where Mahon brought Emily Kaye no longer exists. The lonely beach where Irene Munro met Field and Gray is now a footpath behind suburban gardens. Generations of British true-crime writers, from Edgar Wallace in the 1920s through to recent BBC documentaries, have made the Crumbles murders part of the literature of interwar England - a moment when newspaper sensationalism, the still-recent trauma of the First World War, and the closeness of Lewes Assizes to Fleet Street combined to make minor murders into national events. But the women at the centre were not literary devices. Irene Munro was a teenager on her first holiday alone. Emily Kaye was thirty-eight, pregnant, and trusting the wrong man. Both stories end, in their separate ways, on the same shingle beach. The shingle has been built over. The names should not be.