Sometime in the past, Max Kleinman awakens to the sound of knocking. A group of vigilantes insists that he join them in a manhunt for a maniacal killer who is strangling people in the streets. Kleinman does not want to go out. He tells his landlady he is hoping to get a promotion at work and cannot afford a sleepless night. The landlady accuses him of kowtowing to his boss, Mr. Paulsen, and suggests that if Kleinman married her, he would not have to worry about money. Kleinman reminds her that he intends to marry his fiancée, Eve. On his way out, the landlady gives him a packet of pepper to use in self-defense. Kleinman goes to meet the vigilantes outside, but they have disappeared. Unsure what he is supposed to do, he talks to himself as he skulks around the dark, foggy streets. Meanwhile, Irmy, a sword swallower in a traveling circus, confronts her boyfriend, a clown named Paul, about wanting to settle down and have children. Paul claims he needs more time alone, and that family is “death to an artist.” He wanders outside and flirts with Marie, a high-wire performer. Marie lures him to her wagon, where her husband, the strongman, has passed out. As she kisses Paul, Irmy barges in and breaks up with him. Elsewhere, Kleinman visits a doctor performing autopsies on several murder victims, who hopes to discover the nature of evil by studying human insides. He wonders aloud why some sane people are driven to be homicidal, while others sublimate bad impulses into creative endeavors. Kleinman asks for a drink, and suggests that perhaps there is something intangible about evil, but the doctor scoffs at the idea of spirituality. Kleinman is repulsed by the sight of a dissected corpse, and leaves. Still unsure what the vigilantes expect of him, he returns to the streets, where one of the vigilantes grabs him from behind and startles him. They discover another murder victim on the ground. Meanwhile, carrying a suitcase filled with her belongings, Irmy wanders into town. She encounters a prostitute, who warns her the streets are unsafe and offers her shelter in a brothel. There, Irmy bonds with several prostitutes, who share their differing views on love and sex. Irmy cannot imagine pretending to feel passion in exchange for money. However, when a group of wealthy students arrives, a young man named Jack declares Irmy the most beautiful woman he has ever seen and offers her the astronomical fee of $700 for sex. Irmy agrees, and actually enjoys her encounter. Meanwhile, the killer attacks the doctor, who claims to feel no fear, but attempts to flee. The killer follows the doctor into the streets and strangles him. Kleinman witnesses the Mintzes, a family of “social undesirables,” being arrested on suspicion of murder, and tells an onlooker that the Mintzes are lovely people. He goes to the police station to speak on their behalf. A policeman arrives with news that the doctor was killed. They believe the killer was in his office, and present the glass from which Kleinman drank as evidence. Kleinman watches nervously as a police officer dusts the glass for fingerprints. Irmy is brought to the police station for prostituting herself without a license, and fined $50. Kleinman witnesses as she repeatedly denies being a prostitute. He takes advantage of the commotion to steal the glass with his fingerprints. Outside, he runs into Irmy, who tells him she is a sword swallower with the circus. Kleinman reveals he is an amateur magician, and offers to take her to his fiancée Eve’s apartment, where she can sleep on the couch. Another vigilante appears and accuses Kleinman of socializing during the manhunt. Kleinman admits he does not know what he is supposed to do. The man suggests he walk down a nearby street where the killer might be lurking. Irmy offers to accompany the frightened Kleinman, who cowers behind her. In a dark corner, Irmy spots a peeping Tom and shrieks, believing he might be the killer. Kleinman attacks the man but is horrified to discover it is his boss, Mr. Paulsen. Although he apologizes profusely, addressing Paulsen as “your majesty,” Paulsen accuses Kleinman of being a simpleton and a detriment to the manhunt. Paul the clown goes in search of Irmy. He stops in a bar and meets Jack, the student who paid her for sex. Jack claims he made love to a woman who was “sheer perfection” and inadvertently reveals the woman to be Irmy when he identifies her as a sword swallower. Paul becomes irate when Jack conjectures that Irmy’s lover is some “poor clown” who never pleased her in bed. Elsewhere, Irmy asks Kleinman to donate her remaining $650 to a church. However, after he drops off the money, they encounter a starving mother and her baby, and Irmy asks him to retrieve half the money. Kleinman takes back $300 and notices the clergyman and a policeman adding his name to a list. Soon after, Kleinman and Irmy arrive outside his fiancée Eve’s apartment. Eve is angry at being woken up and refuses to allow Irmy to spend the night. Kleinman complains to Irmy that Eve is a “cold fish.” They stop walking and admire the stars just visible through the fog. Irmy explains that, although the light is just reaching them, many of the stars no longer exist. Kleinman is unsettled by things that are not as they appear. A mob arrives with a clairvoyant named Spiro, who believes he can find the killer. Spiro demands to smell Kleinman, and as he takes a whiff, announces that something is hidden in Kleinman’s jacket. Someone removes the glass Kleinman stole and identifies it as a missing piece of evidence. Kleinman tosses the pepper from his landlady into the crowd and flees. He takes refuge at the home of Alma, to whom he was once engaged, but she yells at him for leaving her at the altar and sleeping with her sister, and forces him out. Paul finds Irmy and threatens to kill her for betraying him, but also begs her to come home. They stumble upon the dead body of the starving mother Irmy gave $300, and discover her abandoned baby nearby. To Paul’s dismay, Irmy vows to keep the baby, and retrieves her $300. Still running from the angry mob, Kleinman takes cover in the brothel. A prostitute lures him into a bedroom, but he is unable to achieve an erection. Police arrive and he flees again. On the streets, he encounters Simon Carr, a co-worker who just received the promotion Kleinman was hoping for. Carr laughingly recounts how Paulsen described Kleinman as “cringing, slimy vermin.” Kleinman goes to the circus in search of Irmy. Meanwhile, Paul has become smitten with the baby and tells Irmy they should have a child of their own to keep the baby company. Irmy goes outside to fetch milk. Just as the killer stalks her, Kleinman arrives and warns her to run inside. Kleinman leads the killer into the circus tent, where he encounters Armstead, the magician, who uses magic tricks to confine the killer to a chair. However, when the vigilantes arrive, the killer has disappeared. Irmy thanks Kleinman for saving her life. She tells him the circus is due to leave tomorrow, and bids him goodbye. Hearing that Kleinman is newly unemployed, Armstead offers him a job as his assistant. Kleinman initially declines, but changes his mind, realizing there is no better way to spend his life than helping Armstead with his wonderful illusions. Armstead agrees, declaring that people need illusions like they need air.