Amy Manning, Kathleen Beller, a 20-year-old art student, leaves work late and discovers a mysterious man in black hiding in her backseat. He has a chance to kill her, but instead leans in and whispers, “Soon, Amy, soon,” before vanishing into the night. The encounter unsettles her deeply, and the police reach a dead end, offering little help as fear tightens its grip on her. Her stepmother Adele Manning, Mariette Hartley, believes her, yet urges Amy to see a psychiatrist, Dr. Letterman, Keir Dullea, hoping therapy might untangle the knot of guilt that haunts her. Amy explains that her father drowned a year earlier during a boating accident; she was supposed to accompany him on that trip but canceled at the last moment, a decision that haunts her still.
One afternoon, a package arrives for Amy with the same chilling card: “Soon, Amy, soon.” Adele and Amy begin tracing the parcel’s origins, which lead to a florist, Milton Selzer, who insists that Amy herself placed the order. Adele then reaches out to James Stockwood, Arlen Dean Snyder, an attorney and a close friend of Amy’s father, to discuss the troubling situation. But James overhears the plan and storms off, sparking a rift in the family. Back at college, the unseen assailant reappears, terrifying Amy as she tries to escape, until a fellow student, David Norland, Gary Graham, materializes and offers help. Amy returns to Dr. Letterman, who attributes her fear to a subconscious creation of a killer she’s inventing, providing a clinical explanation that shifts some of the weight off her shoulders. Despite this, Amy decides to confront the roots of her guilt by returning to the cabin in the woods where her father died.
Adele accompanies her at first, but a tense encounter with James reveals that he’s worried about Amy’s impending inheritance—she stands to receive her father’s estate in three months, which could leave him and his associates in need. Adele pretends to care about Amy’s welfare, yet it becomes clear she’s part of a larger scheme to break Amy’s resistance. Letterman, somehow involved in the plot, heads to the cabin where a confrontation unfolds, and after a struggle, he sedates Amy, places her on a boat, and pushes her into the river. He then returns to Adele, offering comfort and absolving her of immediate guilt, even as she wrestles with the disturbing events she’s endured.
Soon after, strange occurrences begin at Adele’s mansion: doors lock and unlock on their own, and a sculpture of Amy vanishes. Adele suspects a malevolent presence but is reassured by Letterman that she’s simply imagining things. A late-night phone call from James reveals that Amy’s body has been found, amplifying the shock. The next night, Amy appears at Adele’s door, and when Letterman arrives, Adele, convinced he’s the intruder posing as Amy, shoots through the door in a fatal miscalculation.
The twist lands with a cold revelation: Amy’s supposed death was part of a calculated ruse by James, David, and Amy to drive Adele into a confession about killing Amy’s father. Adele is arrested, and Amy, now free to live with David Norland, celebrates a fragile two-month partnership. In the final scene, David whispers the same chilling refrain, “Soon, Amy, soon,” sealing the bond and the game that brought them all together.
