The show's main characters are FBI special agents Fox Mulder (David Duchovny) and Dana Scully (Gillian Anderson), who work on cases linked to the paranormal, called X-Files. Mulder is a believer in the paranormal, while the skeptical Scully has been assigned to debunk his work. In this episode, Mulder and Scully investigate a series of ritualistic killings by somebody seemingly capable of squeezing his body through impossibly narrow gaps. The agents deduce that their suspect may be a genetic mutant who has been killing in sprees for ninety years.