Julia Lofting, portrayed by Mia Farrow, finds herself in a tragic situation after her young daughter Kate, played by Sophie Ward, chokes on a piece of apple during breakfast. Despite her desperate attempts to save her, including a botched tracheotomy, Kate tragically succumbs to her injury, leaving Julia devastated and alone. She decides to leave her husband, Magnus, portrayed by Keir Dullea, and relocates to an eerie old row house in a less favorable part of London.
Once settled, Julia discovers a room laden with a child's belongings and comes across a peculiar mechanical clown with sharp, clanking cymbals, which ends up injuring her finger. Odd occurrences plague her new home; she soon believes she’s glimpsed Kate in a nearby park, only for the vision to vanish. The unsettling atmosphere becomes further compounded by strange noises she attributes to Magnus, whom she suspects is spying on her. When she attempts to photograph the child’s items, the developed pictures reveal nothing, and she experiences bizarre phenomena, such as a radiator mysteriously activating.
As Julia grapples with her reality, she is invited by Magnus' sister, Lily, to host a séance in her home with the medium, Mrs. Fludd. However, things take a turn for the worse when Mrs. Fludd, frightened by unseen forces, warns Julia to leave. The situation escalates when one of Lily’s friends, Miss Pinner, has a fatal accident falling down the stairs shortly after the séance.
As Julia tries to make sense of the haunting nature of her new residence, Magnus attempts to check on her but meets with a tragic fate himself after a mysterious fall in the basement. A neighbor informs Julia that her house was once owned by Heather Rudge, who similarly lost her daughter, Olivia, to choking. This connection leads Julia to delve deeper into the past, uncovering disturbing truths regarding Olivia's friends, all of whom seem to bear the burden of tragic memories.
Julia's investigation leads her to confront the remaining adults connected to the incidents, including Captain Paul Winter and David Swift. Winter dismisses her claims, while Swift reveals the sinister influence Olivia wielded over the children. The tension escalates when Julia experiences supernatural encounters with Olivia’s spirit, culminating in terrifying events that claim the lives of those around her, including her friend Mark, played by Tom Conti.
Desperate for answers, Julia visits Mrs. Rudge in a psychiatric facility, where she learns that Mrs. Rudge was driven to murder Olivia after the horrific events unfolded. As Julia races against time to uncover the truth, she finds herself drawn deeper into the darkness. Ultimately, she confronts Olivia's spirit and tries to offer solace, only to find herself facing a tragic end. In a haunting finale, Julia bleeds to death, her throat seemingly cut by the sharp cymbals of the mechanical clown, leaving a trail of sorrow and unanswered questions in the aftermath.
