East of France, December 1917. In a village situated close to the front but protected from it by a hillside, the body of Belle de Jour, a little girl, is found by the canal. Judge Mierck, assisted by an Colonel Matzev representing the Armed Forces, investigates the case in his own way. The fact that the young victim's corpse lies a few yards from the manor of Destinat, the withdrawn, haughty-looking district attorney, who has always despised and humiliated him, doesn't escape him. To make matters worse, a witness has seen the magistrate not only talking with Belle but patting her cheek as well minutes before the little girl was strangled. But vengeance is one thing and class privilege another...