Somewhere in the universe, the “Borrower,” a brutal killer, is given human form and banished to Earth. He is advised to take care of his new body, as any damage may result in a “painful metamorphosis.” The creature lands in a wildlife preserve near Chicago, Illinois, and attempts to kill the insect-like pilot of his spacecraft. Deer poachers Bob Laney and his son, Kip, come to the assistance of what they believe to be a fellow human, and frighten away the pilot. When the killer turns on the father and son, his head explodes. Bob believes he can sell the headless body as a medical curiosity, and sends Kip to borrow a neighbor’s van. Moments later, the body comes to life and replaces its head with Bob’s. In Chicago, police detectives Diana Pierce and Charles Krieger capture a violent rapist named Scully, who sustains a gunshot wound while resisting arrest. Meanwhile, a young woman named Astrid drives the Borrower into the city, oblivious to his throbbing cranium and strange mannerisms. At the police station, Kip Laney recounts the events at the wildlife preserve, but Charles Krieger dismisses the story, believing the young man is a drug addict. The Borrower is befriended by Julius Caesar Roosevelt, a homeless man who invites him to breakfast at a soup kitchen. A vagrant named Ruben Whitefeather interrupts their meal to beg for money, and responds to their refusal by placing a dead rat in the Borrower’s food. The alien is unfazed as he eats the rat, until Julius orders him to spit it out. That evening, Julius and Ruben introduce the Borrower to liquor, which causes his head to explode. He replaces Bob’s head with that of Julius and feeds on the body. Ruben runs to the police station and describes the incident, but Charles dismisses the story as the ravings of an alcoholic. Meanwhile Scully escapes from custody after beating and raping policewoman Michelle Chodiss. At the city morgue, a coroner named Connie informs Charles and Diana that she has discovered a nonhuman blood type among the remains of the Borrower’s victims. Charles disregards her suggestion of an alien killer, arguing that the murders were the result of human depravity. The Borrower awakens in a hospital after drinking himself into a stupor, and assumes both the identity and the head of resident physician Dr. Cheever. Accessing the doctor’s memory, the Borrower drives to Cheever’s home and removes the head of his dog, Vlad. In an adjacent house, Astrid videotapes a rock band, whose members complain about the barking dog. The Borrower attacks Lance, the singer, but Astrid subdues the creature with a shotgun and summons police. After investigating the scene, Charles and Diana are ordered by their superior, Captain Scarcelli, to send the carcass of the “dog-headed monster” to the morgue. Later that night, Scully breaks into Diana’s bedroom, but she surprises the rapist and shoots him to death. In the morning, Diana and Charles are notified by Connie that the Borrower is still alive. They rush to the morgue to find Connie possessed by the alien and feeding on Scully’s corpse. Charles shoots the creature several times through the head, but within moments, the Borrower takes control of Scully’s body and attacks the detective. Agents of the Federal Bureau of Investigation (FBI) come to Charles’s rescue and fire on the Borrower. Ignoring Diana’s warnings that the creature may not be dead, the agents take custody of the Borrower, and are killed while transporting him in an ambulance.