Mothers' Instinct (2018) on Netflix

Plot summary

In the early 1960s, Alice Brunelle and Céline Geniot are close friends, and their two families live in matching houses and spend their days together. Their sons, Theo and Maxime, have grown up like brothers. That shared life ends when Maxime, Céline's boy, drops from the window of his bedroom. It happens in an instant, and Alice, who is there and sees it, cannot reach him in time. Céline is overcome by grief and holds Alice responsible for the loss of her child. Her manner toward the family next door changes, and the closeness the two households once had begins to come apart.