A dying man enters the office of Éric Besson, a lawyer in Paris’s 13th arrondissement. He is carrying a dilapidated notebook full of meticulous investment records. For decades, he has been helping a cadre of dirty cops launder stolen money. The notebook contains his full confession. He is adamant that Besson get the notebook into the hands of La Proc, Paris’s chief prosecuting attorney, so the corruption can finally be brought to light. But en route to La Proc, Besson’s courier --- his assistant and nephew --- is murdered, and the notebook disappears. Private investigator Aimée Leduc is reluctant to get involved, as her father was a cop and was murdered by the same dirty syndicate the notebook implicates.