In Paris, a young girl is found dead in a Parisian square, wearing an evening dress. Commissioner Maigret will try to identify her and then understand what happened to the victim.

Inviting the ex-wife to a family reunion when the none-too-secure new wife will be there hardly seems to be a recipe for success, and true to form, bodies have begun to stack up by the end of this cinematic update of a classic Agatha Christie tale. Luckily for the extended clan gathered at a sumptuous waterfront estate in Northern France, Inspector Martin Bataille is on hand to find out not only "who done it" but why.

Victim of vertigo and unexplained discomfort, Flavie, a television host, resolves to consult a psychiatrist. The latter suggests a test of the past that she would have concealed and proposes to browse together a photo-album of her childhood. The cliché of a teenager with a sad look will wake up buried memories ...

Louise, a widow with two children, almost crushes a stranger with her car. She takes care of him, even if he's not really wounded. It turns out that he has mental disorders and that they can help each other much more than they thought.