The apparently mentally disabled Davide falls into the canal and drowns. As it turns out, he had an overdose of beta blockers in his bloodstream. Ana Cavanelli, Davide's mother, confesses to Brunetti that she gave him the pills - Davide had asked her to die several times. When Brunetti receives a hint that there is a connection between Davide and the multimillionaire Ludovico Lembo, he gradually uncovers the abysses of a family tragedy.