Captain Nolan (Richard Harris) is an Irish Canadian fisherman who catches marine animals and sells them in order to pay off the mortgage of his boat so he can return to Ireland. Nolan's crew is looking for a great white shark for a local aquarium, but a scientist named Ken (Robert Carradine) is being targeted by the shark. An orca killer whale comes and kills the shark, subsequently saving Ken. This switches Nolan's target to the orca. While Nolan is on the journey with his crew, he tries to capture what he believes to be a bull orca, but mistakenly harpoons a pregnant female. Nolan and his crew get the orca on board, where she subsequently miscarries. The crew hoses the dead fetus overboard as the male looks on screaming.
Seeking release of his near-dead mate, the male orca tries to sink the ship. One of Nolan's crew members, Novak (Keenan Wynn), cuts the female off the ship, but the male leaps and drags him into the sea, eating him alive. The following day, the orca pushes his now dead mate onto shore. Alan Swain (Scott Walker) berates Nolan on his actions after finding the dead whale. Nolan denies responsibility, but Swain and the villagers eventually find out his involvement. The villagers insist that he kill the orca, as its presence is causing the fish vital to the village's economy to migrate. The orca then terrorizes the village by sinking fishing boats in broad daylight and then breaking fuel lines, thus destroying the village's fuel reserves and causing a massive fire.
Dr. Rachel Bedford (Charlotte Rampling), a colleague of Ken and whale expert, shows him how similar whales are to humans and tells Nolan that, "If he (the orca) is like a human, what he wants isn't necessarily what he should have." Nolan confesses to Rachel that he empathises with the whale, as his own wife and unborn child had previously been killed in a car crash caused by a drunk driver. Nolan promises Rachel not to fight the whale, but the orca attacks his sea-front house, containing an injured crew member of Nolan's, Annie (Bo Derek) within it. The house starts slipping into the sea and the whale bites Annie's leg off. Nolan decides to fight the orca, although with Novak dead and Annie maimed for life, Nolan and Paul (Peter Hooten) are now the only crew members left. Dr. Bedford and Ken join the pursuit, along with a native American man, Jacob Umilak (Will Sampson), enlisted for his orca knowledge.
The crew begins to chase the whale after it signals Nolan to follow him. Ken is leaning over the side when the whale surfaces and grabs him, eating him alive in the process. They follow the whale until they reach the Strait of Belle Isle, though when Paul starts to get into a lifeboat, the maddened orca knocks Paul out of the boat and drowns him.
The next day, the whale shoves an iceberg into the boat and starts to sink it. Nolan manages to harpoon the whale just before he and Dr. Bedford escape from the boat, while Umilak is crushed beneath an avalanche of ice just after sending out an SOS.
Nolan and Dr. Bedford hide in an iceberg, although Nolan slips onto another. The orca separates the icebergs, trapping Nolan. The whale jumps onto the ice, causing it to tilt and send Nolan into the water. The whale lifts Nolan up with his tail and throws him onto another iceberg, killing him. Dr. Bedford looks on as the dead Nolan slips into the water in a cross shape. With his revenge complete, the whale swims southward under the ice, while a helicopter is seen to rescue Dr. Bedford.