Syria, 1937: Hercule Poirot is one of several people present at an archaeological dig to find the skull of St John the Baptist, led by the exuberant Lord Boynton and his loyal son Leonard. The enterprise has been financed by Boynton's rich, rude and overbearing American wife. She bullies her three adopted children, Carol, Jinny and Raymond, as well as the family's nanny. Sarah King, a young English doctor, falls for Raymond and would love to tear him from his mother's apron-strings, and another doctor, Dr Gerard, takes an interest in Jinny, as does a Polish nun, who, with Jinny, is subject to an attack - by white slavers, according to the independent travel-writer Dame Celia Westholme. A mysterious young American, Jefferson Cope, whose link to the Boyntons seems tenuous, completes the group. Only his Lordship has any love for his wife so that, when she is found stabbed to death one blisteringly hot afternoon, Poirot has more than his fair share of suspects to interrogate.