Naturalist Hank Donner, studying whales with his assistant Deke, witnesses two salmon fishermen, Joe and Burt, pursuing killer whales, a species that feeds on salmon. The fishermen shoot a female whale, which, followed by her mate, swims into the cove that Hank has rented. When the wounded female dies, her mate stays in the cove. Hank decides to study the whale and with a 200-ft. net bought from general store owner Kate Rand, who sells it to him despite the protests of the villagers, blocks off the entrance from the sea to the cove. The whale, belying the reputation of its species, becomes friendly with Hank and allows him to ride on its back. The good-natured whale is instrumental in dispelling the fear of the sea held by Kate's young daughter, Lisa, whose father drowned while skin-diving. Hank and Lisa christen the whale Namu. One day Lisa and her friends are feeding Namu when a sadistic boy secretly tosses Namu a fishhead imbedded with barbed hooks, and the whale's pained thrashing destroys the dock on which the children are standing. Two of the children are only mildly scratched, but the villagers use the incident as an excuse to demand Namu's destruction. Hank produces the barbed fishhead but the villagers are not dissuaded from their judgment until both Hank and Kate get into the water and play with Namu. Joe and Burt, however, begin to shoot at Namu from outside the cove. Deke opens the net, and Namu swims out, hits the boat, and knocks Joe unconscious and into the water. Namu holds Joe above the surface until Hank rescues him, then swims seaward as the onlookers watch a female whale join him. The two vanish in the distance.
