While wind surfing near the seaside community of Port Harbor, a young man is killed by a giant Great White Shark. Author Peter Benton and professional shark hunter Ron Hammer realize the truth, but ambitious governor William Wells refuses to accept that a shark threatens their community. Fearing that a canceled wind-surfing regatta would derail his gubernatorial campaign, Wells has shark nets installed. But the sounds of teenagers splashing in the surf leads the shark to rip through the nets. The next day, the shark plows through the wind surfers, knocking them off their boards. But rather than eat the scattered teenagers, the shark targets the governor's aide and eats him.
The governor can no longer hide the truth. Benton and Hammer head out on the sea, planning to feed the shark dynamite and cause it to explode. But the shark traps them in a cave, and the men have to use their dynamite just to escape. Meanwhile, Benton's daughter Jenny and some of her friends head out on a yacht, armed with some steak and a shotgun, intending to shoot the shark. Instead, its powerful bites on the bait knocks Jenny into the water. Her friends pull her aboard, but not until the shark bites off one of her legs. Governor Wells's son was one of the friends she went out with, and Benton blames him for her injury. Determined to do something right, Wells sets out in a helicopter armed with a steak, apparently intending to hoist the shark into the air and suffocate it. But the shark is too powerful; when it bites into the steak dangling from a winch, it shakes the copter and knocks Wells into the sea. The shark then bites him in half then lunges into the helicopter, dragging it into the sea.
Benton and Hammer go back out to blow up the shark. After an argument, Benton agrees to allow Hammer to be the one to go down with the dynamite strapped into a belt around his waist. Thinking the shark might be hiding in the downed helicopter, Hammer investigates it. But the shark sneaks up on him and attacks. Benton dives in to save him, but Hammer becomes wrapped up in a line and is towed to his death by the shark.
Meanwhile, a shark hunter chains some spare ribs to the side of a dock. The man, a TV cameraman med Bob Martin and some spectators go stand on the dock. The shark takes the spare ribs, towing the dock out into the ocean. Suddenly, the shark begins to attacking the dock, knocking the spectators into the water. It eats the shark hunter and a TV Cameraman, but the others clamber back onto the dock. Benton arrives and rescues the others but gets trapped on the dock when the shark arrives to drag it further out to sea. Hammer's corpse floats by, Benton feeds it to the shark. Benton realizes he has the detonator in his hand. Leaping into the ocean, he flips the switch, detonating the dynamite and blowing the shark's head off.
Back on shore, Benton punches Bob Martin, then gets in a car and drives away.
What does Benton realize he has in his hand?
Detonator