A young tourist loses contact with her group in a Swiss valley not far from Zurich, takes refuge in a remote chalet, and is mysteriously murdered. The police search is futile. Not long afterward, Jennifer, an American teenager, daughter of a famous actor abandoned by his wife, is sent to a Zurich boarding school run by bitter teachers. She hears from Sophie, her roommate, stories of little girls who have disappeared near the school and never been found. That same night, Jennifer relapses into sleepwalking, from which she thought she had recovered, and to escape the mysterious killer she glimpsed in the darkness, she takes refuge in the home of an elderly paralyzed entomologist, assisted by a pet monkey, where she discovers she can communicate with insects. The following night, during a bout of sleepwalking, a firefly leads her to the body of Sophie, who, having gone out disguised as Jennifer to meet her boyfriend, has fallen victim to the monster. After undergoing some medical tests, Jennifer risks being committed to a mental institution. She runs away from the boarding school and seeks refuge again with the entomologist, who, having discovered her mysterious affinity for insects, gives her the "sarcophagous fly" in a cage, advising her to let the insect guide her in her search for the killer. From that moment, Jennifer experiences a series of horrifying adventures, among corpse remains and repugnant insect larvae, until her last night in Zurich, during which horrific events unfold at a relentless pace, leaving her no respite. Who will save her from the mysterious killer?
