The Loyalties — Delphine de Vigan

Adults are as lost as the children they should be protecting, as the lives of four people trapped in a conspiracy of silence hurtle toward a desperate and devastating act.
Twelve-year-old Théo and his friend Mathis have a secret. Their teacher, Hélène, suspects something is not right with Théo and becomes obsessed with rescuing him, casting aside her professionalism to the point of no return.
Cécile, mother of Mathis, discovers something horrifying on her husband's computer that makes her question whether she has ever truly known him.
Respectable facades are peeled away as the lives of these four characters collide, moving rapidly toward a shocking conclusion. Delphine de Vigan has crafted a lean, darkly gripping, and compulsively readable novel about lies, loneliness, and loyalties.