Oh Mercy!

Louis, a young police inspector, takes up a new position in Roubaix, a formerly prosperous industrial town on the border with Belgium. Together with his superior, Inspector Daoud, who grew up in Roubaix and knows the town like the back of his hand, he investigates an apartment fire that was set in a somewhat run-down neighborhood. Two young neighbors and possible witnesses, Claude and Marie, initially refuse to make a statement to the police, but then have a tip about who might have done it. However, the suspects they identify all have alibis. A few days later, the police receive a call from the two women: they are concerned that something is going on in the neighboring house. An 80-year-old woman is found dead, presumably not of natural causes. During the police investigation, it emerges that Claude and Marie were in the neighboring house on the evening of the crime. What were they doing there and, more importantly, did they have anything to do with the murder?