Case 137 is seemingly just another case for Stéphanie, an investigator at the IGPN, the police of the police. But an unexpected element will trouble Stéphanie and transform case 137 into something more than a simple number.
1809, France. Captain Neuville is called to the front, leaving his future bride heartbroken. Her sister decides to write letters on his behalf to cheer her up. But it all goes south when Neuville reappears.