Captain Wallace Caswell, the constable of the small fishing town of Panama City, Florida, has become widely publicized for his crusade to kill the "killers of the sea," those large predatory fish, including shark, sawfish and octopus, which are rapidly destroying the game fish of Southern U.S. waters and wrecking nets of local fishermen. Caswell and a small crew sail aboard the Princess , a thirty-two mast schooner, to the Gulf of Mexico. They see a harmless finback whale, and Caswell, for sport, catches a marlin, which breaks the line and gets away. The lookout man then spies a school of porpoises, which indicates that a "killer" is near. When the men spot a rare bottlenose whale, Caswell takes off his pants, the signal that he means business, then dives in and wrestles the creature, trying to keep its head up so it cannot dive. After a noose is thrown around the whale's tail to hoist it to the deck, the line breaks. The whale is harpooned, and two crewmen follow it in a small boat, but the whale capsizes it and escapes. After the sailors catch giant sea bass, a hammerhead shark is harpooned, and its neck is hacked to break its backbone. When "Evolution" Henderson, the black one-legged cook, sees a tiger shark, Caswell removes his pants, dives in and kills it with his knife. While a diver descends to explore something that the ship has hit, Caswell wrestles a large fighting turtle. After the diver discovers a wreck complete with an ancient chest and skeleton, a giant turtle bites his air line and an octopus embraces him, but Caswell rescues the diver by knifing the octopus' ink sack. While fighting a sawfish, Caswell is slashed in his right leg by the teeth of the saw, and newspaper headlines report that he may be fatally wounded, but after a stay in the hospital, Caswell recovers to continue killing killers of the sea.
