Hercule Poirot is in his hotel room in Jerusalem when he overhears two people discussing a murder. He finds that these two people, Raymond Boynton and his sister Carol, are discussing their stepmother, a sadistic, manipulative, demanding head of a wealthy family. The family is part of the expedition Poirot is taking to Petra.
All of the family are traumatized by their mother’s behavior. Raymond and Carol are eager to escape from their stepmother’s control. Their sister Ginevra is barely attached to reality. Lennox, the oldest son, rarely speaks, and his wife Nadine is threatening to leave him.
Poirot finds the rest of the party in the camp at Petra interesting. Sarah King is a studying psychiatrist who is romantically interested in Raymond, but Raymond does not have the courage to tell his mother. Dr. Gerard is a famous French psychiatrist. Lady Westholme is a well-known politician, and she is accompanied by her friend Miss Pierce.
When Mrs. Boynton dies, the cause is not clear. She was overweight and in poor health. Did she die of natural causes, or was she murdered? If she was murdered, there are plenty of suspects in their party, most of them in her own family. Colonel Carbury, an official assigned to the case who is known to Poirot, asks him to help.
This novel is not one of Christie’s best, even though she continues to deftly draw believable characters. It is marred by some silly psychobabble that was probably popular at the time. Perhaps Christie was trying to reflect then-modern topics of conversation, or perhaps she was writing dialogue that would be typical of the two psychiatrists. In addition, she pulls one of her tricks, making the solution depend upon information that is not possible for the reader to know.