De Chalonge's true story of mass murder in Occupied Paris has Dr Petiot stalking the city like a Nosferatu reborn, surrounding his murders with an obsessive theatrical ritual to a scratchy tango accompaniment. Self-conscious cinematic trickery - all expressionist chiaroscuro and silent-era iris shots - makes an unsettling frame for Petiot's career. The factual part is that Petiot ran a roaring trade persuading Jews that he could ship them safely to Argentina; after handing over their possessions, they ended up in his oven rather than Hitler's. Grisly as the tale is, de Chalonge gives it an almost comic air of Grand Guignol. A hideously flamboyant Serrault plays the killer as a Demon King with kohled eyes and flapping coat-tails. Yet there's a real sense of history, of the emergence from the night of Occupation into the tainted daylight of Liberation. This is a powerfully idiosyncratic shadow-show, an inventively cold-blooded inquiry into the way war breeds monsters - and an unqualified marrow-chiller to boot.