When Myriam, a brilliant lawyer, decides to return to work, she and her husband look for a nanny for their two young children. They never dreamed they would find Louise: a quiet, polite and devoted woman who sings to their children, cleans the family's chic Paris apartment, stays late without complaint and hosts enviable birthday parties. But as the couple and their nanny become more and more dependent on each other, jealousy, resentment and suspicions increase, until Myriam and Paul's idyllic domesticity is shattered...