Crime boss Victor Slidell arrives at a Caribbean airport, where his assistant, Harry Bonner, shows him a picture of a man named Hardy. Slidell orders Bonner to drive him to Hardy’s house. Meanwhile, Brian Hardy puts his girl friend, Paula Stafford, onto a small pleasure cruiser boat and tells her he will call after he gets to Mexico. Hardy then takes his yacht, the Princess Patricia II, out to open sea, where he calls the Coast Guard, claiming his vessel is on fire. A few moments later, the boat explodes. Slidell reaches Hardy’s house and is confronted by a machete-wielding caretaker. Bonner smashes the man’s head through a window, killing him. Slidell and Bonner search the house, but find nothing. A few weeks later, yachtsman Mark Rogers and his crewman, Frank Keeler, are becalmed off the coast of Florida where they are transporting the dead body of Wendell L. Baxter, whose corpse is stowed in the cabin. Keeler cannot stand the smell and demands they toss the corpse overboard. As a reluctant Rogers complies, the wind picks up and they sail for home. In Florida, Keeler and Rogers sit through a Coast Guard inquiry. Rogers explains that Baxter died of a heart attack and they itemized his belongings, which consist of a suitcase, clothes, a few dollars, and a book on sailing. Afterward, Keeler is paid the wages due him and goes ashore while Rogers removes a small refrigerator from the boat that he sends out for repairs. Rogers receives a telephone call from Paula Stafford who tells him that she has not heard from Hardy, and is worried. When Rogers seems to have no idea what Paula is talking about, so Paula plans to fly down to meet him face to face. That night, Keeler arrives at the yacht with Jackie, a much younger woman. Finding Rogers gone, Keeler breaks into the yacht to search for something, but returns to his car empty-handed, where he is attacked by Harry Bonner and his henchman. Later that night, teenagers find Keeler’s dead body on the beach. The next day, Rogers is taken to the police station and questioned about Keeler’s murder, but he tells them little about the man. He is shocked when Lt. Willets says that Keeler had $4000 on him. The interrogation is interrupted by a phone call from FBI agent Soames, who demands to know why Baxter used a false identity. Rogers explains that Baxter showed up when he was docked in Panama and offered to crew his boat for passage to the States. Later that night, another boat bumps into Roger’s yacht. Jackie comes forward, apologizes and asks Rogers to come aboard her vessel to help her understand her charts. When he does, he is knocked out by a blow to the head, and awakens to find himself sitting in the boat’s stateroom. Slidell steps forward and demands to know where Baxter is. Rogers insists Baxter is dead, but Slidell tells him that Keeler reported that Baxter is in Mexico. When a loud noise distracts the tormentors, Rogers bursts out of the cabin, leaps overboard and swims for shore. Rogers returns to find his yacht ransacked. The Marina manager gives Rogers a message from Paula to see her as soon as possible. At her hotel room, Rogers learns that Baxter and Hardy are the same man. Paula shows him a letter that explains that Hardy was carrying $40 thousand to bribe a skipper to take him to Mexico. When Rogers insists Baxter is dead, Paula decides Rogers murdered her lover and attacks him. Rogers throws her to the floor and escapes. Later, Paula is stabbed to death by an intruder. The next morning, Rogers calls a reporter friend, Bill, explains his problem, and asks the newsman to track down information on Hardy. Rogers then flies to the Virgin Islands, and takes a taxi to town, but a car chase ensues. Rogers leaps out of the cab and onto a ferry, and his pursuers follow, but Rogers jumps onto the dock just as the ferry pulls away. Later, Rogers and Bill fly to St. Thomas. On the way, Bill explains that Hardy was a rich yachtsman who blew up in the Princess Patricia II. Rogers realizes that the explosion was a ruse. They go to Hardy’s house and find the same book on boating that Baxter had in his suitcase. The book jacket shows the author, Pat Reagan, on a yacht called the Patricia Princess. Rogers telephones Pat, who claims she never heard of Baxter or Hardy. When Rogers describes the man, Pat says it sounds like her dead father, then hangs up. Rogers finds her St. Thomas address and confronts Pat on the beach. She explains that her father, Clifford Reagan, was a banker who died when his car crashed into Lake Meade, Nevada. Just then, Bonner appears with a gun and takes his prisoners to another yacht, where Slidell waits. As Rogers is tied to a chair, Slidell explains that Reagan was supposed to fence a fortune in stolen bonds, but instead he stole the bonds and ran away to St. Thomas. Under intense questioning, Rogers realizes that when Keeler was below deck nursing Baxter, he found the $40,000 and hid it on the boat, but he cannot figure out how Keeler was able to sneak the money past him as he had no luggage. Slidell asks what equipment Rogers sent ashore and Rogers remembers the refrigerator. Although Rogers and Pat are locked below deck, Rogers finds a flare gun, kicks out a panel, and climbs onto the deck where he sneaks up on Slidell. The old man sees him in a window’s reflection and knocks Rogers down with a chain. Slidell pulls out a knife to finish Rogers off, but trips and impales himself. When the skipper comes out shooting, Rogers kills him with the flare. Another thug attempts to attack Rogers, but impales himself on an anchor. As Rogers tries to push the attacker overboard, the man grabs him and they end up in the sea. The two battle as the boat sails away. Rogers is cut as he struggles with the dying man, but finally breaks free and swims to the surface, only to find his blood is attracting sharks. Meanwhile, Pat escapes from the cabin and sees a Coast Guard helicopter. They radio that a man is overboard and guide her to Rogers. She throws Rogers a line and retrieves him from the water as the sharks attack. Pat and Rogers make love as the boat sails to Florida. Once back onshore, Pat, Rogers, agent Soames and Lt. Willett retrieve Rogers’ refrigerator. They find the remaining $40,000 hidden in its door. They also discover a key to a safe deposit box that contains the stolen bonds. Later, back at the Marina, Rogers wishes his friend Bill farewell and sails off alone.