When Simeon Lee, a mean-spirited, tyrannical patriarch of a dysfunctional family, summons his offspring to his country manor house in Kent for Christmas, he employs Poirot to attend the reunion. The detective is not given a full explanation for his assignment, but he soon observes the palpable animosity, suspicion, and resentment among the three Lee sons. Also in attendance is the beautiful Pilar Estravados, the only surviving child of Lee's daughter, who recently passed away after living in exile in Spain. The ruthless Senior Lee, who made his fortune in the South African diamond fields, sadistically treats his progeny with deliberate cruelty and obviously relishes pitting one against the other. It comes as no surprise when the old man's throat is mysteriously cut in an apparently locked room, and although he was frail and wheelchair-bound, there appears to be evidence of a great struggle. Poirot is aided in his quest for a solution to the baffling mystery by Chief Inspector Japp and local Superinendent Sugden.