A shy, obsessive comic book fan gets injected with an experimental serum of a lab that is studying how to give humans the abilities of spiders. At first he develops minor abilities such as increased strength, which allows him to fight local criminals and bullies, thus living out his dream of being a superhero, and impressing his attractive next-door neighbor. Things start to get more odd when he is able to shoot webs out of his abdomen. Then he loses control over the force with which he applies his increasingly deadly abilities, as well as his judgment to discern between criminals and jokesters. His dream becomes a nightmare when he starts growing large spider body parts, he's in constant pain, and he develops a nearly insatiable hunger. A detective with a traumatized wife begins investigating when bodies covered in cobwebs and spider venom start piling up.