Born with a gap of just ten months, July and September are inseparable; they don’t need anyone but each other. After an incident of bullying at school, the girls move with their mother into a large family house by the coast that had long stood empty. In their new life, so far removed from everything and everyone, July discovers that the nature of their relationship with her sister is gradually—and in an unexpected way—changing. In the house, an atmosphere of fear and anxiety settles in. The girls push the limits of what’s allowed in their games until they trigger a chain of shocking events that lead to frightening discoveries about their past and future.