Mareta Percival, Beulah Koale, is a Samoan New Zealander and a devoted primary school teacher in Aranui, a low‑income Christchurch suburb. On the day of the 2011 Christchurch earthquake, Mareta’s daughter auditions at the CTV Building and is killed, leaving Mareta grief‑stricken and struggling to hold onto her Roman Catholic faith.
In 2014, to keep her unemployment benefits, her nephew and social worker Sio, Dalip Sondhi, convinces Mareta to apply for a substitute teaching post at St Francis School, a largely Pākehā private school with conservative expectations. Despite reservations from the school board, the retiring headmaster Alan Hubbard, Dalip Sondhi, hires her.
One day, Mareta walks in on Sophie, Antonia Robinson, being confronted by deputy principal Peter Wadsworth to specialize in an instrument, and Mareta covers for her by saying they had discussed vocal scholarships. With no choir to begin with, Mareta convinces the headmaster to start one, appointing herself choirmaster, much to the dismay of Peter. She also enlists the help of St Francis alumni and accomplished chorister Helen, Tania Nolan.
The choir attracts several students beyond Sophie, including Anthony Bull, Zac O'Meagher, Mei-Ling, Talia Pua, and Luke, Caleb Nazzer. Despite their privileged backgrounds, these students bring personal traumas and insecurities that the group begins to share and navigate together, learning to work as a team. Seeing potential in Sophie, Mareta trains her as lead chorister.
With encouragement from a local priest, the St Francis choir conducts their first performance at Mareta’s Samoan church. Mareta’s former teaching colleague, Rona, confronts her, viewing St Francis kids as privileged and elite; Mareta collapses and is hospitalized, revealing a cancer diagnosis she had kept hidden.
Mareta introduces her students to the upcoming national Big Sing competition, hoping they will compete. However, due to a troubled home life, Sophie leaves the choir after refusing to don a lavalava because of a disfiguring arm injury, forcing Mei-Ling to take on a leadership role. Tensions rise when Anthony and Mei-Ling are embroiled in a fight with St Francis’ elite rugby team, leading Anthony to leave the choir.
Despite these obstacles and Mareta’s worsening cancer, the St Francis choir presses on and defies expectations, qualifying for the semi‑final and then the final of the Big Sing. Yet Mareta’s teaching contract is terminated, and she is hospitalised as her condition worsens. The choristers remain determined to perform, with Sophie and Anthony returning to the group. To fill the gap left by Mareta, Sophie enlists her mother Caroline, a board member, and Rona’s support. On the night of the final, Mareta passes away, but Sophie leads the St Francis choir, wearing a lavalava, in a moving performance of a traditional Samoan song.
