In 1903, Emmeline, her cousin Richard Lestrange and uncle Arthur Lestrange sail on a clipper ship bound for San Francisco, California, when a fire breaks out. In the confusion, the children are loaded onto one lifeboat with Mr. Paddy Button, the ship’s cook, while Arthur is directed onto another boat. As fog descends, the boats are separated. Soon, Paddy saves a trunk that floats nearby, and after a few days, the lifeboat drifts toward a tropical island. On shore, Emmeline, Richard, and Paddy find food to eat and discover a waterfall perfect for swimming. Afterward, the children gaze out on the ocean hoping to see Arthur’s boat, but it is nowhere to be found. By day, Paddy teaches Richard to fish, to make rope and to tie knots. They build a shelter from bamboo and swim in the warm water. During a walk, Paddy discovers bloody human remains discarded on a boulder. Later, he insists the children never venture to the other side of the island and scares them with tales about the bogeyman. To fill their days, the children play dress up with clothes from the trunk, and Paddy gets drunk from rum found on the island. One morning, the children see Paddy asleep on the beach of a neighboring islet, but when they row over to him, they discover he is dead. Without Paddy to protect them, they load up the boat to leave but find another island nearby to inhabit. With the skills Paddy taught them, they build a bamboo hut, fish, and sew. To celebrate Christmas, Richard hangs stockings filled with pearls he has found in the ocean. Emmeline confesses that she thinks about Richard all the time, but when he asks her to explain what she means, she is unable to talk about her feelings. Instead, she thanks him for the pearls with a kiss. They attempt to sing Christmas carols, but cannot remember the words. One day while swimming, Emmeline leaves a trail of blood and panics, crying out for Richard. However, when he sees that she is bleeding and suggests she might be hurt, she assures him that she is fine. Richard is skeptical and accuses her of keeping secrets. Soon, Emmeline stares at Richard as he builds a raft on the beach. When he wants to know why she is staring, she explains that she is looking at his muscles. Richard accuses Emmeline of becoming strange in ways he does not understand. Life goes on. Now teenagers, Emmeline and Richard wonder if they will ever be found, and if there is a God. At dinner, Richard is lost in thought, so Emmeline does her best to cheer him up. In the midst of their laughter, they hear something. Richard vows to kill anyone who harms them. When a storm leaves Richard and Emmeline housebound, she pokes him with a spear when he repeatedly plays the same song on a handmade musical instrument. Richard chases Emmeline around the hut, tackling her and threatening punishment until she utters a series of compliments about his manhood. One day, Emmeline investigates some noises and finds a huge stone statue with a face carved into it. A trail of blood oozes from the statue. Emmeline believes it is really God, and wants to pray to it. Later, Emmeline has nightmares and when Richard comforts her with kisses, she pushes him away. Confused, Richard caresses a sleeping Emmeline and she again rejects his advances. Richard and Emmeline stop speaking. When Richard sees a ship on the water, he gathers wood for a bonfire, which Emmeline fails to light. The ship disappears, and an angry Richard launches a raft he has built, but it capsizes a few feet from shore. Upon his return to the island, the cousins fight because Emmeline does not believe they will be rescued. Richard disagrees, and admits that he cannot bear to be with her anymore. Afterward, they live separately. When Emmeline becomes ill after injuring her foot in the ocean, Richard confesses that he is no longer angry and would be lost without her. They consummate their love and sometime later, Emmeline has a bout of morning sickness. She confesses that she has lost her appetite for sex and they both feel her stomach move. At night, Richard finds Emmeline in labor but does not understand why she is in pain until she gives birth. As the baby named Paddy grows, it rejects solid food, but suckles Emmeline’s breast and proves to be a natural swimmer. Paddy learns about the animals on the island, builds sandcastles and speaks his first words. One day, Arthur sails on a boat near the island and sees his son, Emmeline and Paddy through a telescope but does not recognize them and leaves. Later, Emmeline sits in the lifeboat on shore with her son. She falls asleep in the boat and is awakened by the sound of Paddy pushing an oar into the water because they have drifted out to sea. Richard hears Emmeline's cries for help and swims to the boat. He climbs in just as Emmeline hits a shark with the second oar. With the shark circling the boat, they are unable to retrieve the oars and drift out to sea. After Paddy eats some poisonous red berries on the boat, Richard divides the remaining berries between himself and Emmeline. The family clutches each other and prepares to die. Then, Arthur’s ship returns and rescues the lifeboat with Emmeline, Richard and Paddy asleep in it.