IT IS probably best to know as little as possible about the plot of this hugely tense French drama before entering the cinema. An unlikely blend of psychological thriller and true-life melodrama, the picture thrives on uncertainty and makes cunning use of the viewer’s misguided preconceptions. It could be the best film Claude Chabrol never made.

We can, perhaps, risk a description of the opening scenario. Catherine Frot, the sad, round- faced star of Le Dîner de Consand The Page Turner, plays the recently separated mother of an apparently well-balanced boy. Her estranged husband wants custody of the child and, when she objects, mysteriously reminds her of some earlier trauma.

One day, she spots her son with a young girl and, for no reason we can immediately discern, develops an obsession with the blonde child. She calls round to her house and, seeing it is for sale, tells the girl’s parents that she might be interested in buying the luxurious property. Things get steadily weirder and more unsettling.

Employing a vague pizzicato score and curious, sweeping camera moves, Safy Nebbou, the youngish director, manages to layer Hitchcockian menace over even the most mundane circumstances. But the key to the film’s notable success is the queasy, unstable chemistry between Frot and, playing the girl’s mother, the gaunt, twitchy Sandrine Bonnaire.

Offering a paradoxical mix of ironclad determination and psychological fragility, Frot, despite her character’s apparent irrationality, secures our sympathy throughout the movie’s steady build-up. Few recent films – and none that weren’t comedies – have done such excruciating things with the dynamics of embarrassment. Reluctantly persuaded to take Frot’s side, we become ever more unnerved by the results of her unshakable fixation.

When the final reversal appears, it becomes clear that a cunning scheme has been afoot to simultaneously nudge us towards several mutually contradictory conclusions. The denouement may seem unlikely, but that is, apparently, what happened in real life. Take nothing for granted.

Directed by Safy Nebbou. Starring Catherine Frot, Sandrine Bonnaire, Wladimir Yordanoff, Antoine Chappey, Michel Aumont, Michèle Moretti Club, IFI, Dublin, 95 min****