Detective Montalbano investigates the murder of a local businessman called Lapecora. Lapecora's widow suspects that he was killed by his lover Karima, a young Tunisian woman who mysteriously disappeared on the day of the murder. After succeeding in tracking down Karima's five-year-old son Francois, Montalbano realises that the case might be linked to that of a Tunisian man, also killed in mysterious circumstances on the same day that Lapecora died. Meanwhile, Montalbano's partner Livia, who has been entrusted with looking after Francois, becomes very attached to the young orphaned boy.