Two sisters, Marguerite Patourel, [Donna Reed], and Marianne Patourel, [Lana Turner], grow up in the 1840s on the English Channel island of Guernsey, daughters of the wealthy Octavius Patourel, each with a very different temperament. Marguerite is gentle and forgiving, a warm presence in the family circle, while Marianne is sharp and calculating, with a clear plan to steer the family shipping business toward greater power and profit. The two young women both fall for the same man, William Ozanne, the son of Dr. Edmond Ozanne, who has only recently returned to the island after years away. Edmond Ozanne is a complicated figure in the backstory: a former teenage lover of Sophie Patourel, Marguerite and Marianne’s mother, whose past romance was fractured by drinking and social differences. Sophie, a woman who married Octavius under pressure from her own parents, carries memories of a love that never quite fit the social circles they now inhabit.
The island’s life is stirred when the clipper ship Green Dolphin arrives in port. Its captain, Captain O'Hara, sings the praises of distant colonies in New Zealand and sways the locals with talk of new opportunities there. The ship also carries a stowaway, Timothy Haslam, who has killed his brother-in-law in self-defense and is given a chance at a new life across the seas. Captain O'Hara sees a chance to help Timothy find a place overseas and agrees to smuggle him to New Zealand. Marianne, ever the schemer, works to get her father to sponsor William as a naval officer, hoping the connection will help the family business and elevate their status. A plan begins to form for a future where William belongs to their world, and the clock looks set to move forward.
After a two-year jump in time, William returns to the island for a day, the weight of all that has happened pressing on him. He quietly proclaims his love for Marguerite, a confession that comes with the sting of loss—their moment is tempered by the sudden death of Edmond Ozanne, William’s father. William must return to his life at sea, traveling to China, where a love letter and a gift for Marguerite are sent, but the voyage ends in misfortune: he is drugged and robbed, misses his ship, and becomes a deserter in the eyes of the authorities. Fate, however, has another plan. He finds the Green Dolphin in a Chinese port and secretly boards it, making his way to New Zealand to stay out of trouble and begin anew. Captain O'Hara finds him work in New Zealand as a schoolteacher, but William’s restless spirit leads him to strike off into the backcountry with Timothy, seeking a life away from the constraints of the island and old loyalties.
Once in New Zealand, William becomes a successful lumberman, creating a new path that allows him to build a life far from the past. A misguided miscommunication then reshapes the entire future: William drafts a letter, written in a moment of drunkenness, proposing marriage to Marianne—an error that Sophie reads aloud to the family. The news stuns Marguerite, who hadn’t realized how close the two sisters’ hopes were to one another. Marianne, eager to claim a future with William, sets off on the Green Dolphin for New Zealand, determined to win him. Captain O'Hara warns her that William’s drunken note may not reflect his true intentions, but her faith in their bond remains unshaken. When the ship nears New Zealand, Marianne learns from O’Hara that William may have written the note under the influence, but she remains steadfast in her decision to pursue him. Timothy, who harbors his own quiet love for Marianne, pushes William into marrying her, ensuring the status quo of the life he believes he deserves—or at least the life Marianne believes she can mold.
On a deathbed, Sophie reveals to Marguerite and Octavius that her own marriage to Edmond was forced and not the dream many remember. Yet she explains that she grew to love Octavius, and she urges Marguerite to see that love can evolve in unexpected directions. Her words carry a final, piercing insight: William was never truly the man for Marguerite, and she can still find a different, better love. Sophie dies, and Marguerite discovers a fresh letter from William announcing Marianne’s pregnancy. The shock of this revelation is compounded by the news that her father has died moments earlier. Grief-stricken, Marguerite retreats to the tidal flats, where she confronts despair as the sea rises. Yet in a moment of stubborn resilience, she finds the strength to climb toward a convent where the sisters take her in, offering shelter and a chance at life again.
Marianne’s life in New Zealand grows in complexity and ambition. Her lumber business is more efficient thanks to a shift toward barge shipping, and she bears a child while managing the family enterprise. But war looms on the horizon between the Maori and the colonial government, and the region becomes unsettled. Timothy warns Marianne and William of the coming danger and urges them to flee, but they refuse and instead fortify their village with a stockade. Timothy leaves for Wellington, seeking safer ground for himself and his friends. A brutal conflict erupts, and the Māori forces seize the family—an act that shakes the couple to their core. Timothy returns and negotiates a release with his Maori allies, and though their timber business lies in ruins, Marianne considers a move to the South Island to start a sheep ranch. Timothy confesses a profound, mutual attraction to Marianne, but she remains steadfast, choosing to stay with William and their daughter.
Meanwhile, Marguerite’s life on the island moves toward a different kind of peace. Back in San Pierre, she returns to the convent with the intention of becoming a nun, while Marianne and William’s life in Dunedin grows into a symbol of achievement. The couple has built a stately home, a thriving sheep business, and a steam-shipping company, and William is recognized as one of the community’s early leaders. Yet Marianne longs to bring the family name back to its origins, and she arranges a pardon so that William can return to San Pierre and help steer the family business once more. When they arrive, Marianne encounters the truth waiting in the letters of the past: William’s confession in China to Marguerite—an admission that his heart spun off in a drunken moment while Marguerite’s devotion to a life of faith remains steadfast. William admits his mistake, and Timothy confirms he knew of it all along. On the day Marguerite finally takes her vows, Marianne meets her and explains William’s past error. Marguerite reveals that she is content in her religious calling, no longer loving William in that romantic way, while William declares to Marianne that his love has deepened for her beyond what he ever felt for Marguerite. The film closes on this note of reconciliation and the quiet resolution of hearts, with Marguerite’s vows marking the final, tranquil act of the tale.
