Barbara Covett is a lonely, aging teacher who becomes deeply infatuated with her new colleague, Sheba Hart, at a London secondary school. Barbara’s life is defined by routine and isolation until Sheba arrives, igniting a fervent desire for connection in Barbara. Sheba, vibrant and struggling with her marriage to older man Richard, finds solace in Barbara’s seemingly harmless friendship. However, Barbara's intentions become clearer when she discovers Sheba's forbidden relationship with a student, Steven Connolly. Barbara seizes this secret as an opportunity to manipulate and bind Sheba closer to herself.

As Barbara builds her web of control, the dynamics between the two women grow increasingly complex and tense. Sheba is torn between her illicit affair and the consequences it brings, while Barbara’s obsession deepens into dangerous territory. Barbara meticulously documents their interactions in a journal, weaving an intricate tale of dependency and power. These confessions not only expose the fragile façade of their friendship but also reveal the extent of Barbara's possessive nature. Through mounting tension and moral ambiguity, the unfolding drama leads to an inevitable confrontation that threatens to shatter both their worlds.