Thea Farmer, 77, a reclusive and difficult retired school principal, lives in isolation with her dog in the Blue Mountains. Her distinguished career ended under a cloud over a decade earlier, following an unspecified scandal involving a much younger male teacher. After losing her savings in the financial crash, she is forced to sell the dream house she had built for her old age and live on in her dilapidated cottage opposite.
Initially extremely resentful and hostile towards Frank and Evelyn, the young couple who buy the new house, she develops a flirtatious friendship with Frank, and then a grudging affinity for his 12-year-old niece, Kim, who lives with them. Thea has never liked children, but she discovers an unexpected bond with the solitary, half-Vietnamese Kim, an awkward, bookish child from a very deprived background. As Thea and Kim become close, Thea begins to find Frank's behavior increasingly irresponsible, and to harbor worries that all is not well in the house.
Her growing suspicions, which may or may not be irrational, start to dominate her life, and build to a catastrophic climax.