Henry is a deeply disturbed drifter, roaming across America and committing indiscriminate acts of murder against men, women, and even children. Settling in Chicago, he makes a brief stop at a diner before he escalates his violent behavior, leading to the brutal killings of elderly shopkeepers and several women at a liquor store.
His prison associate, Otis, picks up his sister, Becky, at O'Hare International Airport and takes her to their shared apartment. That night, curiosity leads Becky to ask Henry about his mother's death—the catalyst for his imprisonment. Henry recounts a disturbing tale where he claims to have stabbed her, a detail that contradicts his earlier assertions of shooting her or killing her with a bat. He shares that her abusive behavior and humiliating acts during his childhood deeply scarred him. In a moment of shared trauma, Becky reveals her own dark past of being raped by her father. This prompts Henry to express a peculiar protection over Becky, as he claims to be disturbed by any form of violence against women. When Otis makes an inappropriate advance toward Becky, Henry's protective nature surfaces violently as he threatens Otis, demanding he never repeat such actions. Despite Becky's evident romantic interest in Henry, he appears to be put off by her advances.
Becky soon finds employment at a salon, completely unaware of the sinister activities that surround her. That very night, Henry and Otis pick up two prostitutes whom Henry stalks and subsequently murders by brutally breaking their necks. Utterly shocked, Otis confronts Henry about his grim lifestyle. In a chilling discussion, Henry tries to convince Otis to embrace his philosophy of murder, claiming there is a relative nature to killing; despite Otis’s concern of being caught, Henry remains confident that everything will eventually work itself out.
Henry introduces Otis to the underground world when Otis destroys their old TV out of frustration. They visit a fence to buy a new TV, but when the rude man ridicules them, it serves as the perfect excuse for Henry to indulge his violent tendencies. He stabs the man with a soldering iron, and in a brutal turn of events, Otis joins in, effectively killing him. Filled with a thrill from their first murder, they steal a high-end TV and a camcorder, leaving without detection.
Soon after, Otis laments a confrontation with a teenager he tried to assault while selling him marijuana. Filled with vengeful desires, he contemplates murder but is advised by Henry to let it go, worried about the repercussions of his actions. Spurred on by the adrenaline of their earlier crimes, the duo embarks on a new killing spree, luring their victims under false pretenses. Henry instructs Otis to mix up their methods to confuse police investigations, explaining that keeping on the move is paramount for a serial killer’s survival. As they watch footage of their previous crime against a suburban family, Otis’s depravity escalates in a grotesque display as he begins to molest the mother’s corpse, but Henry swiftly puts a stop to it.
Becky eventually decides to leave her job and return to her daughter after hearing about her ex-husband being imprisoned for murder. Tensions between Otis and Henry rise after a camera incident involving Otis filming women from the apartment window. Following an evening out where Becky tries to rekindle romance with Henry, their plans are interrupted by Otis. After stepping out to buy cigarettes, Henry is tempted to kill a passerby but saves himself from the impulse. Upon returning home, however, he is horrified to witness Otis attacking Becky. In a brutal struggle, Henry fights Otis, but Otis gains the upper hand until Becky unexpectedly stabs him in the eye with a comb. Seizing the moment, Henry brutally kills Otis and dismembers the body in the bathtub.
In the wake of their violent resolve, Henry and Becky dispose of Otis's remains in trash bags, throwing them into the river as they flee the city. With the promise of escape, Henry suggests they drive to his sister's ranch in San Bernardino, California, reassuring Becky that they will send for her daughter when they settle. As they travel together, Becky professes her love for Henry, who reciprocates in a chilling, detached manner with, “I guess I love you too.” They rent a motel for the night, but the following morning, Henry departs alone, callously driving away without Becky before unloading her blood-stained suitcase into a ditch.
