Greta Evans, an American nanny, takes a job in a remote English village to escape her troubled past. She arrives at the Heelshire mansion and is introduced to her new charge, Brahms, an 8-year-old boy. To her surprise, Brahms is not a real child but a life-sized porcelain doll that the elderly Heelshire couple treats as their son to cope with the loss of their real Brahms years ago. They leave Greta with a strict list of rules to follow, including no visitors, no covering Brahms' face, and reading to him loudly. Initially amused and dismissive, Greta soon experiences unsettling occurrences, as objects move independently and strange noises echo through the mansion.

Gradually realizing that something is not right with the doll, Greta's skepticism turns into fear. Local grocery delivery man Malcolm becomes her confidant, growing increasingly concerned for her well-being. As unusual incidents escalate, Greta starts believing that Brahms’ spirit might inhabit the doll. Her dedication to following the rules intensifies after discovering haunting secrets about the Heelshires' past. However, the disturbing truth unravels in ways she could never have imagined, leading to terrifying and unexpected revelations that explain Brahms' eerie presence and deepen Greta's predicament.