Sittaford is a tiny village on the fringe of Dartmoor. Mrs Willett and her daughter Violet are the newly installed tenants of Sittaford House, a residence owned by Trevelyan, a retired Navy captain. They invite four people to tea on Friday afternoon: Captain Trevelyan’s long-standing friend, Major Burnaby, Mr Rycroft, Mr Ronnie Garfield, and Mr Duke. At the suggestion of Mr Garfield, the six of them decide to play a game of table-turning. During this séance, at 5.25 pm, a spirit announces that Captain Trevelyan has just been murdered. Concerned for the Captain’s safety in Exhampton, Major Burnaby says that he intends to walk the six miles there. There is a thick layer of snow on the ground and further heavy snowfall is forecast for later that evening. There is no telephone in Sittaford, and cars cannot manoeuvre in these conditions.
Two and a half hours later, just before 8 pm, in the middle of a blizzard, Major Burnaby is trudging up the path to the front door of Hazelmoor, the house in Exhampton where Captain Trevelyan now lives. When nobody answers the door, he fetches the local police and a doctor. They enter the house through the open study window at the back, and find Captain Trevelyan’s dead body on the floor. Dr Warren estimates the time of death at between 5 and 6 pm. A fracture of the base of the skull is the cause of death. The weapon was a green baize tube full of sand.
Captain Trevelyan’s will states that, apart from £100 for his servant Evans, his property is to be equally divided among four people: his sister Jennifer Gardner, his nephew James Pearson, his niece Sylvia Dering, and his nephew Brian Pearson (the three children of his other, deceased sister). Each of these four will inherit approximately £20,000. James Pearson is arrested for murder because he was in Exhampton at the time of the murder, trying unsuccessfully to get a loan from Captain Trevelyan.
While the official investigation is led by Inspector Narracott, James Pearson’s fiancée Emily Trefusis starts sleuthing herself. She is assisted by Charles Enderby, a Daily Wire journalist who, after the murder, presented a cheque for £5,000 to Major Burnaby for winning the newspaper’s football competition in Exhampton. Emily and Charles stay with Mr and Mrs Curtis in Sittaford, searching for clues. Mr Dacres, James Pearson’s solicitor, tells Emily that things look much worse than they already imagined. James has “borrowed” money from his firm to speculate in stocks without the knowledge of the firm.
There are several red herrings. Brian Pearson came under suspicion when Enderby discovered him making a late-night rendezvous with Violet Willett; he is Violet’s fiancé. He was not in Australia but had returned to England on the same boat with the Willetts. The Willetts’ motive for moving into the isolated Sittaford house had no connection with Captain Trevelyan. They wanted to live close to Dartmoor Prison, where Violet’s father was imprisoned. His escape from the prison three days after the murder was engineered by Brian Pearson. He and Brian would live with the Willetts as their manservants until the danger passed, but the prisoner was recaptured. Martin Dering created a false alibi because his wife Sylvia was watching him for divorce proceedings. Sylvia is Mr Rycroft’s niece; Jennifer Gardner is Mr Garfield’s godmother; and Mr Duke is an ex-Chief-Inspector of Scotland Yard.
Emily solves the mystery in Hazelmoor after finding Captain Trevelyan’s ski boots hidden in the chimney, and two pairs of skis in different sizes. Major Burnaby is the killer. He engineered the table movements during the séance to make the spirit convey the message that Captain Trevelyan had been murdered. Instead of walking the six miles in two and a half hours after the séance, he went to his own house to put on skis, and skied the distance in about 10 minutes. He killed Captain Trevelyan at about a quarter to six. Then he cleaned his skis and put them in the cupboard. He hid Trevelyan’s ski boots in the chimney to prevent the police seeing them, and thus possibly realising how quickly a person on skis could have travelled between Sittaford and Exhampton. Major Burnaby hoped that the second pair of skis, of a different size, would pass unnoticed.
Mr Rycroft, who is a member of the Psychical Research Society, reassembles five of the six original participants for a second séance at Sittaford House, the absent Mr Duke being replaced by Brian Pearson. The séance has scarcely begun, when Inspector Narracott steps in, in the company of Emily and Mr Duke, and charges Major Burnaby with the murder of Captain Trevelyan. Emily explains that Burnaby had lost a lot of money by buying rotten shares; his motive for the murder was to keep the cheque for £5,000. He had received the letter notifying him of the win on the morning of the day of the murder, contrary to what he told Enderby. Captain Trevelyan had won the competition but used Burnaby’s name to send in competition solutions. In the final chapter Emily turns down a marriage proposal by Enderby – who has fallen in love with her during the investigation – because she still loves her fiancé James.