Frances Austen, Sandy Dennis, inherits her late parents' Vancouver apartment and soon spots a quiet, nineteen-year-old boy sitting in the rain outside a nearby park. He does not speak, yet there’s a sense that he understands more than words can convey. Frances brings him inside, runs a bath, serves a warm meal, and offers a bed in her spare room, quietly locking the door when night falls. The next day, she buys him fresh clothes, setting a careful boundary around their budding routine.
That night the boy slips away, briefly visiting his parents and younger siblings, then heads to a houseboat owned by his older sister Nina, Susanne Benton. He shares what happened with Nina and her boyfriend Nick, David Garfield. Although the boy can speak, Nina explains that he often chooses silence. The three of them exchange cookies—homemade by Nina—that secretly contain cannabis, a detail neither Frances nor her visitor seems to notice as the atmosphere grows more intimate.
The following day, the boy returns with more of the same cookies and unexpectedly encounters Frances’ maid. Mrs. Parnell. Frances welcomes him again and tells Mrs. Parnell to leave early. The cookies are burnt, yet Frances opens an expensive bottle of wine to accompany them; the true nature of the treats escapes them both. Frances becomes absorbed in one-sided conversations and playful flirting with the boy, developing a growing attachment that unsettles the quiet balance she has tried to maintain.
The next morning Frances must go out and will not return until evening. While she’s away, Nina slips in through the spare-room window, takes a bath, and pulls her half-dressed brother into the water. Frances has had a contraceptive diaphragm fitted at a local clinic and later joins a lawn bowls outing with friends significantly older than herself. A doctor from the group, Charles, offers romantic and sexual advances when she returns home, but she rejects him, insisting that she is not attracted to him.
Back in the dark spare room, a shape under the bedclothes appears. Frances speaks to the boy about Charles, explaining that he has long desired her, while she repeats that she is not drawn to him, that he smells old and repels her. Eventually she lies down and asks the boy to make love to her, only to discover that no one else is there—the supposed companion is merely a bundle of dolls and stuffed toys.
The boy slips back to his room and finds all doors and windows nailed shut. Frances apologizes, but insists that she wants things to stay as they are, leaving him imprisoned as she goes out to a bar. She spots a woman sitting alone and invites her to spend the night with the boy, but the woman grows unsettled. A bystander helps Frances locate a prostitute named Sylvia, Luana Anders, at a nearby diner. Frances brings Sylvia home and locks her in the room with the boy, then listens at the door as they have sex. Overcome with emotion, Frances enters the room and stabs Sylvia through the heart.
The boy desperately searches for an exit, but Frances reassures him that he can stay with her and need not fear. As the credits roll, she kisses him repeatedly and tells him she wants him to make love to her while he remains in a horrified state.
