If you’re up for a bit of borderline farcical pantomime that manages to merge elements of Laurel and Hardy with Ingmar Bergman by way of “Mary Poppins” then this is the film for you. It’s set amidst the sand dunes of the coast of La Manche where folks have begun to mysteriously disappear. Drafted in to investigate is the avuncular “Insp. Machin” (Didier Després) and his sidekick “Malfoy” (Cyril Rigaux). They quickly settle their investigation on a confluence of the sea and the Slack river, where a family of subsistence oyster farmers live under the gaze of the mansion of the wealthy “Van…