Blinded by an explosion, Nick Parker stumbles through a Vietnamese swamp, calling out to his friend, Frank Devereaux. He steps into a ground trap and is pulled into the trees. Friendly villagers nurse him back to health, teach him samurai-like sword techniques, and train him to sharpen his remaining four senses so that eventually, when a gourd is tossed his way, he can slice it into four pieces in mid-air. Twenty years later, in Miami, Florida, Nick walks along a highway with a pole-like, wooden sheath carrying his sword. Hearing flies, he steps over dog droppings, and notices that a sunning alligator is not going to attack him. Stopping at a bar, he is harassed by a gang of toughs and knocks them all unconscious using only the sheath. Meanwhile, in Reno, Nevada, Claude MacCready, Ed Cobb, and Slag dangle Frank Devereaux by the feet from the roof of MacCready’s Silver State Casino. MacCready tells Devereaux he owes too much money to repay in cash, but as an organic chemist, he can work off his debt by manufacturing designer drugs. When Frank refuses, MacCready reminds him that he knows the whereabouts of his wife, Lynn, and son, Billy. In Miami, as Nick arrives at the Devereaux house, Billy accidentally drops his homemade clay dinosaur out a second-story window and Nick catches it with one hand. He introduces himself to Lynn Devereaux as Frank’s Vietnam buddy, but she knows Nick only as a name Frank showed her on the Vietnam Memorial to fallen soldiers in Washington, D.C. He explains that he was missing and thought dead for many years. Lynn informs Nick that she divorced Frank and he is now a chemist in Nevada. Two policemen arrive at the house looking for Billy, and Nick, suspicious of their behavior, challenges them. A third man, Slag, walks in and grabs Billy as he comes downstairs. Nick kills the two police imposters with his sword, but Slag shoots Lynn, knocks Billy unconscious, and escapes. With her last breath, Lynn makes Nick promise to take Billy to his father. The boy awakens in Nick’s arms on the way to the bus station. Billy wants to telephone his mother, but Nick says she will contact him later. As the Trans Continental bus pulls out, Slag stands nearby. In Reno, Frank’s girl friend, Annie Winchester, brings his personal effects to the room in which he is held prisoner. Frank is distressed because the newspaper reported his ex-wife is dead and his son missing. On the bus, Billy finds a photograph of his father with Nick when they were soldiers. Nick explains that they were best friends, but got separated during a Vietnamese mortar attack, and never saw each other again. During a bus stop in Kansas, when Billy tries to telephone his mother, Nick explains that she is dead. Billy runs into a cornfield, and Nick follows. At that moment, Slag and a group of killers arrive in a truck and run into the cornfield with guns drawn. Nick picks them off, one by one. Slag grabs Billy and locks him in a shed, but Nick slices him from face to belly, and releases Billy. After they hurry away, Slag wakes up and checks the life-saving mesh vest under his shirt. Later, after Slag calls MacCready with the news that the martial arts expert escaped with Billy, the Silver State owner decides to get a fighting expert of his own. He confesses to Cobb that he has only two more days to repay loans on his casino, or local gangsters will take it away from him, so he demands that Frank manufacture the designer drugs before then. At a campfire, Billy cries and says his father does not want him, but Nick convinces him otherwise. They hitch a ride with a truck driver, who drops them off at Frank’s Reno apartment. When Annie opens the door and welcomes them inside, two brothers, Lyle and Tector Pike, grab Billy and knock Nick unconscious. They tie them up, put them into the back of a panel truck, and force Annie to ride in front with them. When Nick awakens, he directs Billy to get a lighter out of his jacket and burn the rope around his wrists. Up front, Lyle tosses Nick’s sword out the window, and Nick recognizes the sound as it hits the pavement. He tells Billy to start counting, and sets a fire that sends smoke into the cab. The brothers stop, and as they open the truck’s rear doors, Nick knocks them out. With Annie at the wheel, they turn the panel truck around, and Nick commands Billy to count backwards from his last number. When Billy reaches “one,” they stop, and Billy finds his sword nearby. Behind them, the Pike brothers pull two old ladies out of a car, steal it, and catch up with the panel truck. When Annie loses her glasses, Nick drives by following Billy’s directions, and after a shootout through town, Nick forces the Pikes to crash into a parked car. Annie takes Nick and Billy to the trailer of her friend, Colleen. Billy wants to go on with Nick, but he tells the boy he will be back soon. Nick takes a taxi cab to the Silver State Casino. Inside, he sits at the bar and listens to sounds and voices. Finally, he hears Cobb and MacCready talking. MacCready is relieved that Frank will have the drugs ready that evening, and Cobb says they need a new chemist with a better attitude. Nick listens as Cobb orders food to his office upstairs and gets into an elevator. Feigning sight, Nick plays the roulette table and wins. The pit boss stops by the table, bets against him, and switches the little white ball on the wheel. Nick hears electronic clicks, and when he loses, he whips out his sword and slices the pit boss’s vest pocket, revealing an electronic gadget. He rips up the wheel and shows that a magnet has been turned on at the losing number. The customers, seeing what happened, revolt against the casino, and Nick slips away. He takes the private elevator to Cobb's office, forces him to surrender the key to where Frank is being kept, and knocks Cobb unconscious. When he finds his old friend in a makeshift laboratory, Frank cannot believe Nick is alive. Nick tells him Billy is waiting. Frank fills a small box with drugs, then sets the lab afire. Getting a taxi outside, they return to Colleen’s trailer, but find her dead and Annie and Billy gone. The telephone rings, and MacCready tells Nick he is holding Annie and Billy at the Winterhaven ski resort in the mountains, and wants Frank to bring the drugs there, because two dealers are waiting. As Frank and Nick take a cable “tramway” up to Winterhaven, Frank prepares “homemade napalm” bombs from soft drink bottles and stuffs them in his pockets. Nick says he knows that Frank ran away that fateful night in Vietnam and left him behind, but he has returned to forgive him. At the top of the tramway, the Pike brothers, Cobb, Slag, and other thugs empty their guns into the cable car as it arrives at the top, but Frank and Nick get away through an escape hatch in the floor. Running through corridors, Nick dispatches the Pike brothers, and it appears that Frank has again run away, leaving Nick on his own. However, when a half-dozen thugs surround Nick in an empty nightclub, Frank tosses his bombs at them, and Nick kills all his attackers. Upstairs, the drug dealers hear the commotion and leave. As Frank and Nick blast through MacCready’s door, Annie and Billy are tied up and MacCready holds a gun to their heads. He introduces Nick to his own Japanese martial arts assassin, and the two experts fight with swords. A sliced electrical line drops into a Jacuzzi, and when the assassin falls into the water, he is electrocuted. Slag attacks, and Nick knocks him through a window to his death a thousand feet below. The next day, Nick accompanies Frank, Annie, and Billy to a bus that will take them to San Francisco, CA. Billy wants Nick to come, but Nick says goodbye and disappears in traffic. The boy chases after him, stops on a small bridge, shouts, “I hate you,” and throws his dinosaur over the side. Below, out of Billy’s sight, Nick catches it with one hand. He hears Billy say, “I’ll miss you.” The bus stops on the bridge and picks him up. Nick walks away with a tear in his eye.