Naomi Watts and Jaeden Lieberher star in this US drama directed by Colin Trevorrow. The film follows waitress and single mother Susan Carpenter (Watts) and her two young sons, eleven-year-old Henry (Lieberher) and eight-year-old Peter (Jacob Tremblay), who live together in a quiet suburban neighbourhood. When not helping his mother with the family accounts or looking out for Peter, the precociously talented Henry focuses his energies in excelling in school, where he has become friendly with his kind-hearted classmate and neighbour Christina (Maddie Ziegler). However, Henry soon becomes concerned with Christina's increasingly withdrawn behaviour and begins to suspect she is being abused by her stepfather, the local police commissioner Glenn Sickleman (Dean Norris). Understanding that they can't go to the authorities for help, Henry recruits Susan and Peter to help him carry out an elaborate plan to help Christina, which he has jotted down in a special book.