In 1954, a Māori teen named Nellie faces an unexpected turn of events when her family sends her to Christchurch following the closure of her hometown's meatworks. With her relative nowhere to be found, Nellie forges a friendship with Daisy, another Māori girl who has endured a harsh upbringing in various foster homes. After an incident involving theft, both girls are dispatched to the Te Motu School for Incorrigible and Delinquent Girls, where they encounter a formidable force in the form of The Matron. This devout Māori woman, having been raised in a Christian orphanage, seeks to mold the girls into ideal subservient housewives through strict reforms, believing that the arrival of Christianity brought by the British aimed to civilize the Māori people.
As the story unfolds, Nellie and Daisy, with the help of a girl named Polly, attempt a daring escape from the reform school but ultimately face capture. In response to advice from a government official, The Matron relocates the entire school to a deserted island that once served as a leper colony. It is here that they meet Lou, a European girl who has been sent to Te Motu after being discovered engaged in a romantic relationship with her female mathematics teacher. Sharing a dilapidated hut, the three girls form a bond while navigating the oppressive environment set by The Matron.
On the island, The Matron's agenda continues with an unyielding focus on instilling her values through a blend of Christian teachings, housework duties, and other chores. She actively suppresses the girls' Māori culture and punishes them for showcasing their identity, such as when they lead a rock and roll dance among peers. During this difficult time, the girls find solace in the companionship of Barry, the friendly groundskeeper, who shows them the remnants of a hut that once belonged to a Chinese leper, a ghost from the past.
As resistance to The Matron’s harsh control grows among the girls, her desperation leads her to enlist a doctor who performs involuntary sterilization on two of the girls in the secluded medical hut. Lou desperately tries to alert her father to the alarming situation, but her efforts are thwarted when her letter is intercepted. Due to the escalating tension and mysterious disappearances, Nellie and Daisy contemplate another escape, but they find themselves divided over Lou’s hesitance to rebel against The Matron’s rule. Complicated loyalties come to light as Lou appears to conform to the oppressive environment even while fostering secret plans of resistance.
A pivotal moment arises when Nellie confronts The Matron over her harsh treatment of Daisy, resulting in Lou unexpectedly punishing Nellie. However, Lou's yoke to The Matron is soon revealed to be mere deception, a clever tactic to distract The Matron while she, Nellie, and Daisy plot their escape. United in their resolve, the trio conspires to set the medical hut ablaze, destroying its malevolent purpose and paving the way to freedom. Under the cover of night, as chaos reigns among the staff, the girls seize their chance, sailing away from the island on a makeshift raft, leaving behind the harsh reality of their confinement and heading toward the horizon, embracing the unknown future as they sail into the sunrise.
