During a somber Christmas season in Roubaix, a middle-aged, French-Algerian detective is investigating the fatal strangulation of a poor, elderly woman in her apartment. Suspicion falls on her next-door neighbors, two young white women with a complicated interpersonal bond.

Taking inspiration from Hitchcock’s The Wrong Man, Arnaud Desplechin mounts an exacting procedural with docudramatic precision. Essaying the workings of a police precinct, Oh Mercy! delights in the details of its caseload, and illuminates the sociopolitical roots of the crimes under investigation.