While wind surfing near an unnamed seaside community, a young man is killed by a giant great white shark with the power to make the sea explode. Author Peter Benton (James Franciscus) and occasionally Irish-accented professional shark hater Ron Hamer (Vic Morrow) realize the truth but ambitious mayor William Wells (Joshua Sinclair) 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 mayor's aide. Using its sea-exploding power, it flips the aide's boat then eats him.
The mayor can no longer hide the truth. Benton and Hamer head out on the sea, planning to stuff dynamite down the shark's throat and cause it to explode. But the crafty, suspiciously wooden looking shark traps them in a cave; the men have to use their dynamite just to escape. Meanwhile, Benton's daughter Jenny (Stefania Girolami Goodwin) 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 knock Jenny into the water. Her friends pull her aboard but not until the shark bites off one of her legs. Mayor 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 goes 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 Hamer go back out to blow up the shark. After an argument, Benton agrees to allow Hamer 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, Hamer investigates it. But the shark sneaks up on him and attacks. Benton dives in to save him, but Hamer becomes wrapped up in a line and is towed to his death by the shark, just like Ahab in Moby Dick.
Meanwhile, someone gets the wise idea to chain some spare ribs to the side of the dock. Then some yahoo in a cowboy hat and denim jacket with majestic embroidered wings shows up. He has a shotgun that shoots special bullets that can blow up a tank. Cowboy Hat, a TV cameraman and some spectators go stand on the dock. The shark takes the spare ribs, towing the surprisingly seaworthy dock out into the ocean. Apparently needing fiber, or perhaps a toothpick, the shark begins to eat the dock. Then it uses its sea-exploding power to knock a hole in the dock and people into the water. It eats Cowboy Hat and TV Cameraman but the others clamber back onto the shockingly still surprisingly seaworthy dock. Benton arrives and rescues the others but for some reason gets trapped on the dock when the shark arrives to drag it further out to sea. Hamer's corpse floats by. Benton cuddles with it, but the shark rips it from his arms. Benton realizes he has the detonator in his hand. Dramatically leaping into the ocean, he flips the switch, detonating the dynamite and knocking the shark's head off.
Back on shore, Benton punches a TV reporter then gets in a car and drives away.