Mafatu is afraid of the ocean. As a young member of the tribe on the Polynesian island Hikueru, a people for whom sailing and fishing are a fundamental way of life, Mafatu’s fear is a major social stigma. Although he experienced the great trauma at the age of three of nearly drowning and seeing his mother die, those around him have little sympathy or understanding for his fears. Even his father is ashamed of the way Mafatu behaves. As a result of his inability to go out in a canoe and fish, Mafatu is left behind to build spears, nets, and other necessary tools.

Other youth his age tease and reject Mafatu, and one night he overhears their taunts and cannot stand it any longer. He doesn’t want to continue to live with his fear and his shame, so he resolves to go out alone and face his inner demons on the sea. Mafatu takes a canoe and with his canine companion Uri and their albatross friend Kivi, he heads out toward the open ocean. Mafatu has not gone prepared however, and a storm nearly destroys his canoe and sweeps away the few things he brought with him, even his clothing. Uri and Mafatu drift in the canoe for days, growing more starved, dehydrated, and sun burnt. Just as it seems all hope is lost, an island appears in the distance. The current carries the canoe towards this island, and although the coral reef surrounding it smashes the canoe, Mafatu and Uri make it to shore alive.

When Mafatu comes to, he drinks some fresh water from a stream and bandages a cut on his leg. Revived by this, he begins to explore his new surroundings. The island has thick jungle and an inactive volcano at its center, and this terrain is strange to Mafatu, who comes from an island of flat plains and few palm trees. Towards the top of the volcano there is a plateau which offers an excellent view of the whole island.

On the other side of the island from the beach upon which he landed, Mafatu discovers a clearing with a pyramid and idol in it. This is a sacred site of sacrifice for the savage eaters-of-men, a cannibalistic tribe of which Mafatu has heard terrible stories. He is extremely frightened, because although there is no one on the island now, they are sure to return at some time. However, he sees a well-made spearhead at the shrine, and knowing it will be very useful to him he snatches it up before running back to the plateau. Mafatu will use this good vantage point to carefully watch out for any sign that the eaters-of-men are returning.

Meanwhile, there is much work for Mafatu to do in order to survive and make himself comfortable on the island. All of his time on Hikueru constructing tools and perfecting those skills is now coming in very handy. He builds a fire to cook his food, and a shelter from bamboo and woven leaves. Mafatu begins to make a new canoe that he can use to return home. He creates all manner of tools, such as nets, fishhooks, bowls, and mats. Mafatu replaces his lost clothing, and creates spears and knifes from a whale skeleton he is lucky to find. He makes a raft to use until the canoe is complete, and a fish trap for catching more food farther offshore.

There is one problem with the fish trap, however, and this is the hammerhead shark that regularly raids the trap before Mafatu can get what he has caught. One day Mafatu goes out with a knife to end this trouble once and for all. When he sees the shark he grows afraid, however, and can do nothing even as the shark completely destroys the fish trap. It isn’t until Uri is knocked into the water that Mafatu is driven to act. He dives in to save his friend from being eaten, and stabs the shark with the knife, succeeding in killing it. Mafatu helps Uri back onto the raft, grateful to have found the courage to rescue his companion.

This is the first of several such victories for Mafatu. One day while climbing to the plateau to look out for the eaters-of-men, a wild boar charges at Mafatu. He wants to run away but instead acts quickly and uses a spear to kill the wild boar. This is a feat of bravery that even the warriors of his tribe have not succeeded in, and Mafatu returns to his campsite for a triumphant feast. He makes a necklace of the boar’s teeth which he cannot wait for his tribe to see.

Once the canoe is finished, Mafatu takes it out to test it and to retrieve that day’s catch from the fish trap. Unfortunately his knife falls into the ocean while he does so. Mafatu dives down to get it back, because he would hate to lose it, but is attacked by a large octopus while he is at the ocean floor by the coral reef. Mafatu stabs wildly at it, and he is quickly becoming desperate as his lungs scream for oxygen. It seems as if the octopus is going to win, when one well-aimed stab hits the creature in its eye. Mafatu makes it back to the canoe, gasping for air.

Distracted by all of these events, Mafatu did not check for the eaters-of-men that day, which was a huge mistake because they arrive the next morning. Mafatu observes the beginning of their ritual at the sacred site, trying to remain hidden, but he is discovered by four of the savages. They chase him back to his beach, where he leaps into his canoe and tries to get away. At first the eaters-of-men swim after him, but then they turn back and follow in their own canoes. They follow Mafatu out into the ocean and pursue him for over a day before finally giving up.

It would seem Mafatu is home free. However, the currents are now working against him, and he has difficulty making any progress towards his island of Hikueru. As days pass the food and water he brought runs out, and Mafatu once more grows dehydrated and weak. Finally, he notices signs of land in the distance, and realizes with great joy and relief that it is his home. On the beach, the people of his tribe have gathered to see this stranger that is approaching. Even his own father does not recognize Mafatu at first, but when they understand who he is they are amazed. Mafatu’s father proudly announces his son’s bravery, and the tale of Mafatu’s adventures is told for generations to come.