In the peaceful, port town of Cypress Beach, California, a compulsively neat and organized police investigator named Scott Turner trains his replacement, David Sutton, before his transfer to the Sacramento Police Department, where Turner hopes he will have more exciting work. At the pier, Turner introduces Sutton to seafood plant owner Walter Boyett and, across the dock, Turner visits his friend Amos Reed, a shipyard junk collector. Although Turner approaches the old man’s houseboat with trepidation, Amos’s imposing Dogue de Bordeaux, Hooch, pins Turner down by the throat. Amos claims that Hooch has affection for Turner, then complains of suspicious activity at Boyett’s plant. As Turner and Sutton drive away, they are called to Pinecone Beach, where siblings Mike and Christine Harper have discovered over $8,000 washed ashore in a plastic bag. Confiscating the money, Turner tells the children’s mother, Mrs. Kathy Harper, that the cash will belong to them if no one claims it, but they must use it for college. That night, back at the pier, Boyett orders his henchman, Zack Gregory, to kill a worker named Ferraday who stole a plastic bag filled with cash. Hearing Hooch’s barks from across the dock, Boyett sends Gregory to Amos’s houseboat, but when the old man refuses Gregory’s bribe to keep quiet, he is stabbed to death. However, Hooch witnesses the killing, jumps through a window and chases Gregory away. Early the next morning, Turner rushes to the scene of his first murder investigation and is saddened by the death of Amos. As Hooch barks from inside the houseboat where he has been confined, federal agents Harley McCabe and Jeff Foster attempt to muscle Turner off the case, but Turner convinces his boss, Chief Howard Hyde, to let him stay on the job an extra week so he and Sutton can find Amos’s killer. When animal control officers claim Hooch is rabid and threaten to shoot him, Turner says the dog is a witness and escorts him to the town’s new veterinarian, Emily Carson. Learning about the murder, Emily encourages Turner to take the dog home and use him to find the killer. The next day at the station, Turner reviews Amos’s autopsy report and determines by the exactness of the stab wound that the murderer was trained in the military. Chief Hyde complains that the investigation is too costly. Later, as Turner shops for dog food, Hooch wrecks his house. When Turner returns to find his order upturned, he goes after Hooch with a gun. Although Hooch runs away, he soon comes back with Emily’s pretty Collie, Camille. Turner returns the dogs to Emily’s home-based clinic, hoping to slip away without Hooch, but Emily sees him and invites him inside. They begin to fall in love. One day, Hooch spots Gregory at the wedding of Boyett’s daughter at a church across the street from the police station. As Hooch chases Gregory into his Cadillac, Turner and Sutton pursue the criminal and discover his identity through his license plate. Learning that Gregory is a former Marine who works for Boyett, Turner suspects he is Amos’s killer and asks Chief Hyde for a search warrant of Boyett’s plant. When the investigation is fruitless, Chief Hyde bids farewell to Turner and hands the case over to Sutton. Later, Turner and Emily make love and Turner decides to observe the plant through the night. He promises Emily that he will stay in town another few days. Although the stakeout is uneventful, Turner and Sutton search the plant again the next morning, this time with Hooch. Turner lets Hooch smell the bag of cash discovered by the Harper kids and the dog soon traces the scent to a box of matching plastic bags. Later, Turner investigates Gregory’s address at a local motel, leaving Hooch in the car. When Turner threatens the manager, he is held at gunpoint by Gregory. Although Gregory forces Turner into the driver’s seat of his Cadillac, Turner intentionally crashes the car into a wall and Hooch restrains Gregory by his throat. Terrified of the dog, Gregory confesses to killing Amos and discloses that Boyett is running a covert operation. After handcuffing Gregory and calling for reinforcements, Turner returns to the plant with Hooch and orders the dog to watch the back door. Just before entering the warehouse, Turner is surprised to see Chief Hyde, who claims that police are waiting nearby to back them up. Once inside, Tuner snatches Hyde’s shotgun and accuses the chief of collaborating with Boyett. Turner fires the weapon into a block of ice, revealing bags of cash hidden inside. Just then, Boyett shuts off the lights. Hyde recovers his weapon and a gunfight ensues. Meanwhile, Hooch finds his way into the building through a skylight and lunges onto Boyett as he aims at Turner, taking a bullet in his chest. Turner returns fire, shooting Boyett in the leg, but he is held up by Hyde. The police chief kills Boyett and demands that Turner keep quiet. Although Turner tries to humor his superior, Hyde cocks his gun; however, Hooch bites Hyde’s leg before he can shoot. As Turner seizes Hyde’s weapon, it discharges, killing the chief. Turner rushes Hooch to Emily’s clinic, but despite Turner’s soothing words and Emily’s attempts to save him, Hooch dies. Sometime later, Turner takes over as Cypress Beach’s police chief, marries Emily, and becomes the proud owner of a litter of puppies that Hooch sired with Camille before he died.