Two dramatically contrasting episodes face Inspector Gautier in his latest mystery: the death by stabbing of the vicar of the fashionable church of Saint Clothilde in the confessional box; and the theft of the Duchesse de Paiva's diamond necklace during the extravagant fête thrown by Armand de Saules to celebrate the eighteenth birthday of his daughter, Marie-Thérèse.

As the inspector investigates Marie-Thérèse's clandestine affair with a somewhat discreditable Italian poet, Daniele Pontana, and her rejection of her parents' choice for a husband, Gautier discovers the two crimes are strangely connected. As is a third, the murder of Pontana's valet Ponzi . . .