George is a diabetic father who moves next door to daughter Zoe Dalton. Zoe seems to have it all, including successful husband Chris, but when she hires an au pair, Sandrine, the beguiling young French woman triggers an unsettling shift in the household as instincts and suspicions arise, hinting at hidden agendas.

Sisters September and July share an intense bond, speaking in a secret language and keeping the outside world at a distance. After September is suspended from school, their mother brings them to a remote house on the Irish coast—where July begins to resist her sister’s increasingly sadistic control.