The film narrates the poignant story of Paikea Apirana, affectionately known as Pai, a 12-year-old girl who stands as the sole surviving heir to her tribe's chieftaincy following the tragic demise of her twin brother and mother during childbirth. According to tribal tradition, the lead role is meant for the first-born son, a direct patrilineal descendant of Paikea, also called Kahutia Te Rangi, who is famed for riding a whale from Hawaiki. Nevertheless, Pai's gender poses a barrier to her rightful claim to leadership.
Initially, Pai's grandfather, Koro Apirana (Cliff Curtis), the tribe's leader, is overwhelmed with grief over the loss of his grandson and scoffs at the idea of having a "worthless" granddaughter. Although he eventually forms a tender bond with Pai, offering her rides to school on his bicycle, resentment simmers as he blames her for the unresolved issues burdening the tribe. In a moment of rebellion against Koro’s maltreatment, Pai considers leaving with her father; yet, she finds herself irresistibly drawn to the sea, feeling a deep connection to the calling of the whales. She compellingly urges her father to turn back, returning to her roots.
Pai's father, instead of stepping up to traditional leadership, opts for a path as an artist in Germany, leaving Pai to navigate her ambitions alone. Despite the familial resistance, Pai earnestly strives to learn the ancestral customs, including songs and dances, fueled by her determination to become a leader—even without a historical precedent for a woman to take on this role.
In his quest for a worthy successor, Koro creates a cultural school exclusively for the boys of the village, instructing them using the sacred taiaha, a traditional fighting stick reserved for males. However, Nanny Flowers (Vicky Haughton) shares a secret with Pai about Koro's late son, her second born, who matched a similar fate in his youth; thus, Pai furtively trains with her uncle. She also discreetly attends Koro’s sessions, where she finds a surprising ally in one of the students, Hemi. However, Koro’s fury escalates when she triumphs in a taiaha duel against Hemi. The rift widens as none of the boys manage to retrieve a rei puta (whale tooth) Koro had cast into the ocean, a task designed to prove one's worthiness for leadership.
In a bid to mend their fractured relationship, Pai invites Koro to attend her school's Mori chants concert. Unbeknownst to them, she has recently clinched an inter-school speech contest with a heartfelt tribute to Koro and their village's traditions. Alas, Koro’s tardiness coincides with a dire situation; multiple right whales have become stranded on the beach near Pai's home. The villagers rally to save them, yet their efforts are futile. This leads Koro to lament his failures. He scolds Pai for attempting to approach the largest whale, asserting that she has already caused enough chaos.
In a stunning turn of events, as Koro steps away, Pai bravely climbs onto the back of the largest whale, successfully coaxing it back to the ocean, which leads the entire pod to follow. The ocean's embrace almost claims her life, yet she prevails. When she emerges, Nanny Flowers reveals to Koro that Pai had indeed retrieved the whale tooth. Recognizing her courage and leadership potential, Koro grants her forgiveness and acknowledges her rightful place as a leader. The climactic conclusion unfolds with a communal celebration, as the village, along with Pai's father, uncle, and grandparents, honors her new status, culminating in a ceremonial launch of the completed waka into the sea for its maiden journey.
