A woman named Kit is helping herself to free coffee in the supermarket when her attention is seized by a striking teenage girl wandering the aisles.

Kit asks the girl — who introduces herself as Sarah Brinker – if she needs help finding something. Sarah asks if Kit can buy her tampons, claiming that her late mother used to buy them for her and that she's too embarrassed to do it herself.

Kit acquiesces, and Sarah thanks her, adding that the man working the register made her uncomfortable. Sarah goes on to say that people often eye her — but in a different way than they do her sister, who is a model.

As the pair walks out of the store, Sarah pulls a stolen box of cupcakes out from her coat. Kit accepts one and recalls that when she was young, she and her friends stole gum from the same store.

Kit agrees to drive Sarah home, but the girl diverts her towards the woods. They park, and Kit follows Sarah through the trees to a clearing, from which they can see through the windows of Sarah's house.

Together, they watch a young woman disrobe. Shortly thereafter, a grey-haired man enters the room. The young woman sprawls out naked on the bed. Sarah tells Kit that the pair is her father and her sister, and that she comes to this vantage point when she wants "to see what's really happening."

Sarah and Kit make the trek to the house before they see anything else, and Kit reluctantly follows Sarah inside. In a few minutes, Sarah's father, Georgie — the grey-haired man — descends. Sarah introduces Kit as her science teacher. Georgie offers Kit a drink, and then embarks on a monologue about the philosopher Lucretius — who Sarah claims was driven mad by a love philter (potion).

Kit imagines Georgie must be a classics scholar. As he talks, she grows more and more "enamored" of him; the thought of the sister lying on naked on the bed, with him standing in the doorway, only increases her attraction.

The sister — Miranda — eventually descends in a robe, and the group sits down for a tense dinner. It comes to light that Sarah lied about Miranda being a model — she once won a modeling contest, but now works at the mall. It seems Sarah also misrepresented the situation surrounding her allegedly deceased mother. Indeed, when Kit expresses her condolences, Miranda acts perplexed, and Georgie apologizes for Sarah's propensity towards "drama."

Sarah grows agitated and threatens to "take a spade out to the garden" — presumably where she thinks she'll find her mother's body buried. She tells her father to stop pretending not to know where his wife is.

Georgie and Miranda go confer in the kitchen, at which point Kit attempts to leave. But Sarah begs her to stay, accusing her sister and father "conspiring." "You're all I have," she says to Kit.

Kit recalls uttering the same words to the man with whom she had an affair. Their relationship failed, and Kit remains in an unhappy relationship with her husband.

Kit ultimately stays at Sarah's house for dessert, and her attraction to Georgie grows. When he leads her to the bathroom, she expects him to embrace her; he does not.

While rifling through the mother's abandoned closet, Kit remembers a newspaper article she read about the missing woman. Her memory strings together a series of cryptic words: "a shoe, an empty purse, blood."

She returns downstairs, and Sarah suddenly declares that Kit is not actually her teacher. Embarrassed, Kit denies this truth, but moves to take her leave. Georgie attempts to give Kit his cardigan on her way out, but she thinks he is attempting to kiss her and pushes him away.

Kit flees the house and finds her car. She drives away in a fitful state of distraction, obsessing over her ex-lover and reflecting on how she understands Lucretius's madness. When she hits something, she simply plows on, later realizing that she will never know whether hers was the car that struck and killed a man that night. The thump could simply have been a deer or a trashcan.