When two Parisian women are shockingly murdered in their homes, the police suspect young accordionist Clément Vauquer, who was seen outside both of the apartments in question. It seems on the surface like an open-and-shut case. But now Clément has disappeared from public view. His likeness has appeared in the papers and detectives from Paris to Nevers are on his tail. To have a chance of proving his innocence, he seeks refuge with old Marthe, a former prostitute and the only mother figure he has known. Marthe calls ex-special investigator Louis Kehlweiler to help Clément. But what Louis uncovers is anything but straightforward, and he must call on some unconventional friends to help him solve his most complex case yet. Not only must Louis try to prove Clément's innocence, he must solve a fiendish riddle to lead him to the killer.