The Sinister Urge

Police Lieutenant Matt Carson and his associate, Sergeant Randy Stone, arrive at a crime scene in the local park. While viewing the body of a young woman in her underwear, they list off similarities to previous murders in the park and suspect a connection to the local \"smut picture racket\".

The next scene takes place in the studio of pornographic director Jaffe. While Jaffe is working, his superior Johnny Ryde brings orders from their boss, Gloria Henderson. She wants their smut inventory moved to a safer location than Jaffe\'s storeroom. Jaffe promises to do so after finishing that day\'s shoot. Almost immediately after Johnny leaves, however, the police raid his studio, arrest everyone, and seize all the films and pictures.

Back at the police station, Carson and Stone are berated by their superior who demands quicker action in exposing the racket. Afterwards, the two officers are visited by local businessman Mr. Romaine, who asks why taxpayers\' money is being wasted in persecuting pornography, which he views as harmless compared to juvenile gangs and violent crime. In response, Carson claims that the dirty picture racket is connected to all major crimes. He shows Romaine pictures of the murder victims and explains the connection between their work and their violent deaths. Shaken, Romaine leaves thinking of his own two daughters.

Gloria is visited by Johnny, who informs her of the recent police raid. Their conversation reveals the woman at the beginning of the film was killed by their lackey Dirk for attempting to blackmail Gloria. Johnny states that he is worried about Dirk, since he clearly enjoys killing with his knife. Their talk moves to their teenage customers\' demand for new bondage photos.

At Jake\'s Pizza Joint, teenagers are enjoying themselves when one man challenges another to a fight. The fight moves outside, surrounded by onlookers. Dirk is seen observing from afar. Back inside, Jake negotiates the purchase of more smut pictures from Janet, an agent of the pornography ring. He complains about the inventory of photos he already has and demands new ones. Janet assures him new ones are coming, and asks him to keep the old ones at the restaurant until they can make a trade. Outside, Dirk tires of the fight and calls the police before fleeing. While responding to the call, the police find Jake\'s supply of smut and arrest him along with the two fighting men, revealed to be rival smut peddlers fighting over the right to sell to Jake.

The scene shifts back to Gloria\'s house. Gloria and Johnny are watching 16 mm films and conversing. Gloria points out that the increasingly unstable Dirk is both aroused and triggered to kill by viewing pornography. Johnny claims that he can still keep the killer under control. Meanwhile, Dirk has returned to the park. He is flirting with a woman and the two kiss, but then he strips off her clothes and stabs her to death.

In the police station, Carson and Stone talk about the type of women who get mixed up in pornography rackets: \'Mary Smiths\' from \'Everywhere, USA\' who graduate at the top of their class, were once great in a school play, come to Hollywood seeking stardom, and are afraid to return home a failure. The film follows the path of one \'Mary Smith\'. The inexperienced actress is rejected by film studios and talent agents, before offered work by Johnny Ryde, who introduces himself as a director. Excited, Mary agrees to work for him. She receives money for her expenses long before filming starts. One day, she\'s called to \"audition\" for a hostile Gloria, who berates both Mary and Johnny for wasting money as a ploy to trick Mary into agreeing to do any type of work to pay back the debt. Mary ends up in Jaffe\'s studio, where he\'s shooting her in cheesecake photos, though he and Johnny discuss how she\'ll soon be in pornography. She ends up getting murdered in the park by Dirk, who found her pictures after breaking in to Gloria\'s house. He accidentally leaves the photos behind, and the police are able to trace his identity through his fingerprints. With Dirk\'s name in the paper, Gloria\'s bosses in \"the Syndicate\" visit her to demand Dirk\'s murder before he gets them into more trouble.

Gloria wants to kill Dirk directly, but Johnny suggests sending Dirk on an errand in a car with faulty brakes so that it appears he had a car accident. The next day, Dirk goes back to the park to stalk another victim. The woman he chooses is actually Officer Kline disguised as a woman on orders from Carson. While Kline is successful in subduing Dirk, Johnny arrives just in time and knocks Kline out. Dirk agrees he needs to leave town for a while and drives off in the faulty car. When the brakes fail in the hills, Dirk survives his \"accident\" by leaping out of the car.

Out for revenge, Dirk makes it to Gloria\'s house. He manages to ambush an arriving Johnny, who claims it was Gloria\'s idea to kill him. He explains the two men could replace Gloria as ringleaders as soon as they got access to her Syndicate contacts. Dirk hides outside as Gloria arrives. Johnny informs her Dirk is alive. He demands he be treated as an equal to Gloria, asking to meet her contacts in The Syndicate. Gloria seemingly agrees and goes to change clothes. Johnny is then stabbed by Dirk in the backyard. Gloria comes back and shoots Dirk, mistaking him for Johnny because of the darkness. She calls the police with a story about how Dirk shot Johnny and then ran away, but they arrest her when they discover both bodies.