Devon Gummersall plays Quentin Kemmer, a shy security guard and obsessive comic-book fan who dreams of becoming a superhero like his favorite character, The Arachnid Avenger, and of dating his next-door neighbor Stephanie Lewis. When his partner is killed during a botched robbery at the research laboratory where he works, Quentin is fired and he injects himself with an experimental serum derived from spiders. The next day he is wracked with a severe fever, spends most of the day unconscious, and, upon waking, discovers that he has gained extraordinary strength.
That same night, Stephanie is stalked and attacked by a would-be assailant. Quentin intervenes and kills the man, then disappears before Stephanie can even glimpse him as her rescuer. Later, Quentin returns to his apartment and learns that Detective Frank Grillo is hoping to identify his savior. Quentin is thrilled to finally realize his dream of becoming a true superhero, but his body continues to mutate; he develops spider-like abilities, including the ability to shoot webs from his abdomen, and his appetite grows insatiable even as solid foods become harder to stomach. One day, while out shopping for something to curb his hunger, he encounters a man attempting to rape a young woman and rips the assailant apart. The woman, however, reveals that the man was her boyfriend, and when she tries to call the authorities, Quentin encases her in webbing. Police Officer Williams arrives to intervene but is attacked by Quentin.
The following day, investigators discover the brutal scene at the store: the victim drained of fluids, the woman in shock, and a strange sign of spider webs along with Williams’s missing badge. Quentin, terrified by how far he has transformed, holes up in his room to keep others safe from him. Yet that very night, driven by hunger, he roams again and murders two young men who used to pick on him. Detective Frank Grillo and the lab-head begin to piece together the possibility that Quentin’s serum is at the heart of the killings, and that the scientist’s attempts to transfer spider properties into humans may have produced the killer.
Frank visits Quentin’s apartment and finds evidence—webbing and the basement filled with bodies encased in silk. Meanwhile, Frank’s wife, Trixie Grillo, who has been having an affair with Officer Williams, follows him to the scene and is attacked by Quentin. Frank arrives in time to rescue her, but she dies in his arms. The tension peaks when Quentin abducts Stephanie and takes her to an abandoned building. Frank finally tracks them down, discovering Stephanie suspended in a giant web as Quentin, now a grotesque fusion of man and spider, confronts him and begs to be put out of his misery. Frank initially refuses, but the animal side of Quentin overpowers him and he opens fire, killing Quentin. Stephanie, who had just moments before expressed gratitude toward her would-be savior, dies in Quentin’s arms after the tragic confrontation.
In the aftermath, Han—a friend of Quentin’s—introduces a comic-book collector to an action figure that resembles his late friend, now reimagined as a superhero named Quentin Arachnid. John Cho appears as Han, who helps bridge the living world with Quentin’s final, haunting legacy.
