A small-town sheriff attempts to clear a Doberman of murder charges.

In the sleepy California coastal town of Eden Landing, police chief Abel Marsh returns from vacation to learn that reclusive divorcée Jenny Campbell has been killed, presumably by her Doberman pinscher. Abel, who has a bemused affection for his small town and its eccentric denizens, visits Dr. Warren G. Watkins, the veterinarian who tranquilized the dog when it was found on the beach guarding Jenny's body. At the office, Abel meets Watkins' new nurse, Kate Bingham, who is angry that the dog, Murphy, is being euthanized despite how well-behaved he is. Sarcastically telling Abel that "they only kill their masters," she makes him view the dog, who responds readily to his commands. She relates that dogs usually attack the throat when killing, making Abel wonder why Jenny's bites were on her extremities. Abel then orders that Jenny be exhumed, and the pathologist states that she was not killed by Murphy. The doctor reveals that Jenny was drowned in fresh water doctored with salt, so that her killer could dump her body in the ocean and make it look as if she drowned there, and also that she was pregnant. Postulating that Murphy, not realizing that Jenny was dead, was trying to rescue her from the ocean, Abel returns to the vet's office. Watkins states that although they have never treated the animal before, they will find him a good home instead of euthanizing him. That night, Abel drives along the coast road, which includes a one-way tunnel signaled by red and green lights. At Jenny's beach house, Abel discovers that the bathroom has been scrupulously cleaned, and that anything that could have confirmed the presence of someone else has been removed. Later, Abel questions Jenny's ex-husband, wealthy playboy Lee Campbell, who reveals that his sexually adventurous wife demanded a divorce after falling in love with another woman. Back at Jenny's house, Abel finds a photograph of a nude man and woman, holding hands and running away from the camera, although he is unable to identify them. Having been summoned by Abel, Kate arrives and he explains that he wanted her help in looking around, as the police force has few scientific resources. Kate, who has softened toward Abel and shares his attraction, confirms that the bathtub was cleaned with industrial disinfectant, and Abel confides that it is probably where Jenny was killed. As they talk, Abel learns that Kate is divorced and that no one will adopt Murphy because they think he is a killer. Despite his self-proclaimed antipathy toward dogs, Abel takes Murphy in and they begin to bond. Kate and Abel's relationship progresses also, and soon they spend the night together. One evening, Abel's date with Kate is interrupted by a summons from Capt. Daniel Streeter, his childhood friend and the head of the sheriff's department. Streeter questions Abel's handling of the murder case but agrees to let him remain in charge. Abel then begins the drive to Jenny's house, at which he is to meet Campbell. During the journey, however, Abel and Murphy are delayed when they have to wait at the one-way tunnel, after which a speeding car rushes through. Abel proceeds to the home, only to find that it has been set on fire, and when he attempts to capture the arsonist, the culprit escapes in Campbell's sports car. When Abel breaks into the bedroom to call the authorities, he finds Campbell, who has been stabbed. By the time the police arrive, Campbell is dead and John, a young patrolman, explains that they were delayed because the sports car was blocking the tunnel. At home, Abel and Kate are talking in bed when Murphy jumps up to sleep with them. While wondering if Murphy did not bark at the arsonist because it was someone familiar to him, Abel taps him on the snout, unaware that it is a command for him to assume attack mode. Kate successfully gets Murphy off the bed, but Abel, spooked, returns him to Watkins. In the morning, Streeter and his deputies arrive to take over the case, and Streeter upbraids Abel about the second murder. As Streeter is talking, he mutters about Murphy's strange name, prompting Abel to wonder how Kate knew the animal's name if he had never been treated at the clinic. Staring at the photo of the naked couple, Abel suspects that the woman is Kate and rushes to her boardinghouse room. There, he tosses her onto her bed and demands to know how she knew Murphy's name. Realizing sadly that he suspects her, Kate relates that it was Watkins who told her, and later, Streeter arrests her on suspicion of conspiracy. Abel drives to the clinic and watches as Watkins plays with Murphy, including tapping him on the snout to make him attack and employing the correct command to stop him. Deducing that Watkins has known Murphy for a long time, Abel arrests him for the murders, but Watkins escapes by injecting Abel with a euthanasia drug. Abel manages to radio in his dilemma but passes out while chasing Watkins. Later, Abel wakes in the hospital and learns from Streeter that the drug was flushed from his system, and Watkins has evaded capture. Abel orders Streeter to release Kate from custody, as he now knows that she is innocent, then staggers out of the hospital. The next morning, Abel tries to find Kate at the clinic but discovers that she has quit and the equipment is being packed by a moving company. When Abel questions Streeter about the search for Watkins, he deduces that the doctor is hiding in his own home and arranges to be boxed into a crate that is delivered to the house, along with the clinic equipment. There, Abel sneaks up on Watkins and levels his gun at him, but Watkins asserts that he did not kill anyone. As they walk downstairs, Watkins' wife hits Abel from behind and Watkins runs outside, where he is shot by Streeter. Abel yells in frustration, as he has realized that Mrs. Watkins, not the doctor, is the killer. Over her husband's dead body, Mrs. Watkins reveals that she was indeed Jenny's lover, but that the voracious Jenny was not content. Jenny seduced the doctor as well and then became pregnant, after which the intensely jealous Mrs. Watkins killed her, and the doctor helped to cover her crime. When Campbell saw the two of them at the beach house, Mrs. Watkins killed him and set fire to the home. Mrs. Watkins is arrested, and soon Murphy has regained his place at Abel's side. Abel is saddened when Kate says goodbye, and he reluctantly admits that he briefly considered her a suspect. After watching her taxi depart, however, Abel radios Streeter and asks him to follow Kate to learn her destination.