In 1977, on the Promenade des Anglais, a war is raging between two casinos: the venerable Palais de la Méditerranée, which brought prosperity to the Riviera and which Renée Le Roux inherited upon her husband's death, and the Ruhl, a flashy new establishment run by a shady clan, linked to the Italian Mafia and the mayor of Nice, Jacques Médecin, seeking to secure a local monopoly on gambling. A lawyer with a troubled personality, Maurice Agnelet convinces his mistress Agnès, 29, the third of the four Le Roux children, to sell her shares to the owners of the Ruhl for 3 million francs, thus sealing her mother's defeat. Four months later, on October 27, the young woman disappears without a trace. Her body will never be found.

In March 2014, thirty-seven years after the disappearance of Agnès Le Roux, a diminished old man appeared, free, at the Rennes Assizes, supported by his youngest son, Thomas. Maurice Agnelet, 76, persists in claiming his innocence.