In a seedy Los Angeles motel, Carl Martin stabs a blonde woman to death. Police detectives Pete and Don investigate and correctly suspect that the murder is related to an unsolved stabbing that occurred one month earlier. Soon after, Carl, a gardener who uses his shears as his murder weapon, shops at a nursery owned by Fred Saunders and finds himself attracted to Fred's blonde daughter, Jane. After Jane, whose husband is in the Army overseas, declines Fred's offer of a ride home, Fred picks up a blonde in a bar and drives beneath a freeway bridge, where he murders her. When two patrolmen stop to investigate, Carl punches one and flees from the other. The officer shoots and Carl returns fire, but manages to escape by jumping onto a passing produce truck. Back at the police station, the patrolmen supply Pete and Don with Carl's description. The detectives question the police psychiatrist, who deduces that Carl is a paranoiac serial killer who targets similar-looking, married blondes under the age of thirty. Pete and Don station blonde policewomen in bars around town to tempt Carl, and soon the killer picks up one of them, a woman named Virginia. Although Carl drives her into the hills planning to murder her, he spots Don tailing the car, and drops Virginia off unharmed. Soon after, the body of another of Carl's victims is found in a riverbed and Pete and Don discover a spring from the shears on the ground near the body. Lab technician Charlie uses the spring to identify the brand of shears, and the police canvas local nurseries. When they arrive at Fred's shop and show him the description of the killer, he identifies Carl and informs them in horror that Jane is at that moment delivering supplies to Carl. Meanwhile, Jane has reached Carl's and discovered that he is the killer. While holding a pair of shears to Jane's back, Carl reveals that mistreatment by his former wife repeatedly induces him into a murderous rage. He holds Jane hostage when Pete and Don arrive, forcing them to drive away, but at the last moment Don slips out of the car and doubles back to the cabin. There, he shoots Carl just before the killer can take Jane's life.