David and Laetitia Brunelle and Sylvain and Tiphaine Geniot are inseparable friends and next-door neighbors in a pretty, tranquil suburb. Their sons Milo and Maxime, born in the same year, grow up together as close as brothers. But when Maxime is killed in an accident, their idyllic world shatters. Maxime's parents, Sylvain and Tiphaine, are consumed by grief and bitterness, while David and Laetitia are wracked with guilt for their role in the tragedy. Soon the couples are barely speaking, although they maintain a polite facade. Then a mysterious series of "accidents" begins to happen to Milo, raising Laetitia's suspicions. Are their former best friends trying to punish them by threatening their son? As an increasingly paranoid Laetitia frantically tries to protect Milo from harm, the little civility left between the two families curdles into outward hostility. Is Laetitia just imagining things? Or are Sylvain and Tiphaine secretly conspiring to exact their revenge . . . and if so, who will pay?