La demoiselle d'honneur (2004)

A middle class family in Loire, where things seem just a tad off kilter. Philippe dotes on his mother, who has raised his two sisters and him. Gérard, a wealthy man just divorced, is paying attention to her, then drops her. Philippe is actually pleased, and retrieves from Gérard's garden a stone head - of the goddess Flora - that his mother had given Gérard. At the wedding of one of his sisters, Philippe meets Senta, a quirky and moody young woman: they fall quickly in love, despite her odd behaviors and Philippe's general good sense. Senta announces a plan for them to prove their love to each other; it involves poetry, tree planting, and murder. What will Philippe do?