“Man is the cruelest animal.” Nietsche

In North Dakota, a woman named Sally Dumont rides a horse to her farm. As Sally guides the animal to a stall in the stable, she discovers another horse, its coat stained with blood, lying on the ground inside its pen. As she kneels down next to it to investigate, Sally notices someone wearing a pair of rubber boots standing in the adjoining stall. Terrified, she makes her way to a phone and calls for help. Suddenly, the intruder looms up from behind and knocks Sally unconscious.

Frank meets with Sheriff Jeff Falkner, who believes the incident does not warrant the Millennium Group’s attention. But Frank notes that twenty-one horses have been killed in the surrounding area during the last two and a half years. He believes that the perpetrator is a psychosexual killer in the making–someone who must be stopped before his sickness compels him to take human life.

Police discover the word “help” written in human blood near the telephone where Sally Dumont placed her call for help. They also discover human semen in the stall next to where the horse was killed. Frank believes the perpetrator was reacting to an entirely new experience: for the first time, he had a woman, and not a horse, in his power.

The perpetrator, a man named Willi Borgsen, uses an electric cattle prod to shock hogs in a tractor trailer oustide of a bar. When approached by the owner of the rig, Willi incapacitates the driver by shocking him with the cattle prod. Police later discover the driver’s beaten body in a wooded area nearby. Upon investigation Frank realizes a set of boot-prints at the scene match the type of footwear worn by the perpetrator. He also concludes that the suspect is incapacitating his victims with an electric cattle prod, a device used by slaughterhouse workers.

The body of another victim, a woman named Mary Ann Wright, is found on a farm with a dead horse nearby. On a barn wall is scrawled the message, “thank you.” Willi telephones Frank using a special number set up by police to report information about the crimes. Willi taunts Frank telling him that committing murder brings him great pleasure.

While discussing the case with Claudia Vaughan, a local veterinarian, Frank is shocked when he sees foals being led to slaughter. Claudia explains that P.M.U., or Pregnant Mares Urine, is the main element in Hormone Replacement Therapy which is the most profitable pharmaceutical in the United States. Mares are deliberately kept pregnant for their urine, and when the animal gives birth, the foal is killed and the meat is shipped overseas. Frank concludes that the killer was raised on a P.M.U. farm.

Willi again telephones Frank. He warns that killing Mary Ann Wright did not satisfy his urges. Frank warns that his bloodlust will only intensify. After Willi hangs up, Frank realizes Claudia Vaughan is his next victim. Falkner, Watts and Frank break down the door of Claudia’s home, but she has vanished. Frank realizes Willi took her to a slaughterhouse that deals in horses.

As the men enter the slaughterhouse, Willi engages a motorized pulley system from which animal carcasses are hung. Falkner sees a still-conscious Claudia swinging among the carcasses, a meat hook through her jacket. Suddenly, Willi steps from the shadows and jolts Falkner with a stun-gun, knocking him to the ground.

Frank searches the slaughterhouse for Willi. The stun-gun is jabbed into Frank’s back, sending him tumbling into a killing box. Willi fires a pneumatic bolt (used to slaughter livestock), narrowly missing his prey. A sheriff’s deputy sneaks up behind Willi, but his boot crunches a fragment of bone. Willi turns, firing a bolt into the deputy’s chest. Frank escapes through a wire mesh at the bottom of the killing box. But Willi gains the upper hand, aiming the gun at Frank’s forehead. Suddenly, a wave of horses charges towards Willi, trampling him.