Among the towering red cliffs and the ancient ruins of Petra sits the corpse of Mrs. Boynton, the cruel and tyrannizing matriarch of the Boynton family. A tiny puncture mark on her wrist is the only sign of the fatal injection that killed her. With only twenty-four hours to solve the mystery, Hercule Poirot recalls a remark he overheard back in Jerusalem: «You do see, don't you, that she's got to be killed?» Mrs. Boynton was, indeed, the most detestable woman he had ever met.