Nearly two decades have passed since the end of World War II, and Thomas Gilhooley, a former United States Navy (USN) veteran, has found himself working aboard a freighter. Realizing that the ship won't dock at his intended destination, Haleakaloha in French Polynesia, he decides to leap into the water and swim to shore.
Meanwhile, Michael Donovan, another USN veteran and a close friend of William "Doc" Dedham, who serves as the only medical doctor in the area, is quite engaged with his life on the islands. When Doc requests that Donovan look after his three children during a two-week trip to provide medical care to the surrounding islands, Donovan readily agrees.
An interesting tradition connects Gilhooley and Donovan, as they share a birthday and have celebrated with a fistfight for over 21 years, much to the entertainment of the locals. This year, they go on to ransack "Donovan's Reef," the bar owned by Donovan.
Back in Boston, Miss Amelia Dedham, a refined young woman of wealth, has taken charge as the chairman of the Dedham Shipping Company after inheriting a significant portion of stock from her father, Doc Dedham, whom she has never met. Determined to uncover evidence that Doc has breached an outdated morality clause in his will, she travels to Haleakaloha to secure her control over the company.
Upon learning of Amelia's imminent arrival, Donovan, Gilhooley, and the Marquis de Lage hatch a plan to maintain their ruse. Donovan will pose as the father of Doc’s three children—Leilani, Sarah, and Luke—until Doc returns to clarify things.
As Amelia digs deeper, she discovers that during the war, her father, Donovan, and Gilhooley were stranded on a Japanese-occupied island, where they engaged in guerrilla warfare with the help of local residents. Among the island’s significant landmarks is a hospital and a large house adorned with a prominent portrait of Doc's late wife, a striking Polynesian woman named Manulani, who passed away giving birth.
Amelia's experience in the islands challenges her preconceived notions. Initially, she and Donovan clash, but she soon reveals herself to be more open-minded than he expected. As they embark on boating adventures, Amelia impresses Donovan with her prowess in water skiing and outswims him to the shore. She grows fond of Donovan's children, inadvertently inviting them to enjoy a Christmas celebration at their home. Gradually, the hostility between Donovan and Amelia gives way to a burgeoning romance, although Lage’s interest in Amelia, both for her affluence and his own motives, complicates matters by sowing doubt about Donovan’s intentions.
When Doc finally returns, Donovan confides the truth about the deception. The long-awaited reunion between father and daughter takes place, during which Doc reveals his wartime sacrifices and how he came to stay in the islands. He generously signs over his stock to Amelia, but before he can share the full details about Manulani and his children, they are interrupted by a hospital emergency.
In a twist of fate, Amelia uncovers the truth: Leilani, as Manulani's daughter, is not only an island princess but also Amelia's half-sister, a revelation celebrated with joy.
After confronting Donovan about his deceit, Amelia feels insulted by his justification and decides to return to Boston. However, persuaded by her father, she seeks Donovan one last time to bid farewell. What begins as an argument fades into marriage plans as the two discover their deep connection, even agreeing to name their first son William in honor of her father. Gilhooley also moves forward, marrying his long-time sweetheart, Miss Lafleur. As a thoughtful gesture, Donovan gifts his bar to Gilhooley as a wedding present, and in a beautiful display of family unity, he starts moving into the grand house, marking the beginning of their extended family life.
