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."

In the studio of pornographic director Jaffe, 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. After Johnny leaves, the police raid his studio, arrest everyone, and seize all the films and pictures.

Carson and Stone are berated by their superior, demanding quicker action in exposing the racket. Local businessman Mr. Romaine visits the two officers, asking why taxpayers' money is being wasted on persecuting pornography, which he views as harmless compared to juvenile gangs and violent crime. 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.

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 enjoy themselves when one man challenges another to a fight. The fight moves outside. Dirk observes 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 smut supply and arrest him along with the two fighting men, revealed to be rival smut peddlers fighting over the right to sell to Jake.

At Gloria's house she and Johnny watch 16 mm films and discuss Dirk. Gloria points out that the increasingly unstable Dirk is 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. The film follows the path of a young woman named Mary Smith. Unable to find legitimate film work, she accepts an offer from Johnny Ryde. One day she is called to "audition" for a hostile Gloria, who reveals that Mary's debt to her can only be paid off by working for her. Mary ends up in Jaffe's studio posing for cheesecake photos, where Jaffe states she'll soon be in pornography. She is later murdered in the park by Dirk, who found her pictures after breaking into Gloria's house. He accidentally leaves the photos behind, and the police 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 successfully subdues Dirk, Johnny arrives just in time and knocks Kline out. Dirk agrees he needs to leave town and drives off in the faulty car. When the brakes fail, Dirk survives his "accident" by leaping out of the vehicle.

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 that the two men could replace Gloria as ringleaders as soon as they access 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. Dirk then stabs Johnny 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.