There’s a dash of Tom Ripley in Sarah, and perhaps a bit of the adolescent mischief maker from Francois Ozon’s recent “In the House,” who insinuates himself with a seemingly picture-perfect family by seeming to be everything their own son is not. But as skillfully embodied by De Laage, there’s an inner sadness to Sarah, too, that makes her impossible to dismiss as a mere sociopath or emotional vampire. It’s a feeling that only intensifies when Laurent finally reveals the truth about who Sarah really is and where she comes from — a scene staged in one breathtaking traveling master shot that goes from room to room along the outside of a house, and which suggests that Laurent’s directorial gifts are hardly limited to her work with actors.