A nameless man set adrift by a storm wakes up on a deserted island, which he discovers is rich in resources. He finds fresh fruit and water, as well as a variety of small animals and a dense bamboo forest, and prepares to leave the island. He builds a raft from bamboo and attempts to sail away. However, an unseen sea creature destroys the raft, forcing him back to the island. He tries again with another, larger raft, but is again foiled by the sea creature. A third attempt again ends with the raft destroyed, but this time he finds a giant red turtle facing him in the water. The turtle does not harm him, and he retreats to the island.That evening, the man sees the red turtle crawling onto the shore, heading inland. In anger, he hits the red turtle about the head with a bamboo stick, then pushes it over onto its back. Partway into building another raft, he feels remorse about leaving the turtle upside-down and tries to flip it back over, but finds it too heavy. He races to get fresh water to revive the turtle, but, realizing it is dead, falls asleep next to it. During the night, the turtle's shell splits down the middle and the man is surprised to see a woman lying unconscious inside the shell. He fetches water for her and builds a shelter to protect her from the sun. When rain hits the island, the woman wakes up. The man notices her gone and searches the island for her, eventually spotting her in the sea. He removes his shirt, leaving it for her on the beach, and retreats. Later, he sees her dragging the now empty turtle shell out to sea and setting it to drift off. He does the same with his half-built raft. The two soon form a romantic bond.An indefinite time later, the couple has a son. The curious boy finds a glass bottle and learns about his origin. After accidentally falling into a small cavern, the boy learns to swim on his own and forms a relationship with some sea turtles. The boy grows up knowing only the island. One day, as he goes inland for fresh water with his bottle, a tsunami hits. No one is severely hurt, but the bamboo forest is nearly demolished. After the three clean up the island and burn the dead bamboo, the boy has a dream of swimming away from the island. He and his parents realize that it is time for him to leave, and he swims away with a trio of green turtles, and is not seen again.The man and the woman continue to live on the island, growing old but still much in love with one another. One night, after gazing at the moon over the ocean, the man closes his eyes and dies. The woman soon realizes his passing and grieves. The next morning she lies next to him with deep sadness, holds his hand one last time, then transforms back into a red turtle and returns to the sea.