Mako and his family live on the island of Bora Bora in the South Pacific. One night, Mako's grandfather tells him of a creature that inhabits the lagoon near the village. This creature, Tupa, has frightened the villagers for many years. King Opu Nui has even offered a reward for Tupa’s capture.
At first, Mako’s mother admonishes Mako and his grandfather for even speaking of Tupa. After momentary consideration, she thinks it is time that Mako learns the truth about his father. His father was one of three fishermen who was killed by the great white shark. Mako vows to kill the shark, to avenge his father and claim the reward.
Mako's mother sends him on an errand, and Mako travels with his dog, Afa, to a nearby island to pick some bananas and oranges. Mako imagines the reef as a great white shark and dreams of defeating Tupa. He has even practiced sending his spear through the “eyes” of the imagined shark.
After collecting bananas and oranges, Mako heads for home. He sees Tupa’s dorsal fin circling the canoe, and Afa barks and moves around in the canoe. Afa falls into the water and is in danger! Mako spears the shark in one eye, and then the other. Mako paddles cautiously toward the weakened shark and delivers a final blow.
Mako ties the shark's tail to the boat and tows it behind his canoe. He brings the shark back home. The villagers are thrilled that Mako has defeated Tupa who has been a fierce predator in the area. Mako is rewarded with thirty acres of land and a canoe after a celebration feast the next day.