Somewhere in the Alps, in a region thought of in folklore as “the Swiss Transylvania”, young tourist Vera Brandt (Fiore Argento) just missed the bus she needed to catch. With no bus coming any time soon, Vera sets off hiking to see if she can find help. Coming across an isolated house, she enters… and somewhere inside the house, someone who’s been chained to the wall breaks their bonds. The unseen prisoner, now freed, slays Brandt and her body falls into a rushing mountain stream, speeding it away from the murder site swiftly.
Eight months later, a string of women of about the same age have disappeared in the area, and the police have only found a few body parts. Inspector Rudolf Geiger (Patrick Bauchau) and his unnamed assistant (Michele Soavi) resort to seeking the help of Professor John McGregor (Donald Pleasance) – a forensic entomologist whose expertise allows him to assess the approximate age of the grisly finds based on the extent to which insects have fed on them and spawned maggots within them.
The Professor has every reason to want to help them; his assistant Greta disappeared some time back, and given the profile of the girls who have disappeared he has every reason to believe she is another victim of the killer. Alas, an accident has left him using a wheelchair – though he’s not without help, especially in the form of his highly talented chimpanzee friend Inga (played by Tanga, also a chimp).
And more help is on the way. Jennifer Corvino (Jennifer Connelly), daughter of Hollywood heartthrob Paul Corvino, has just arrived in the area to take up a place in the Richard Wagner International School For Girls, a private school based out of one of the buildings in Wagner’s old estate, as staff member Frau Brückner (Daria Nicolodi) is proud to declare. Jennifer has a tendency to sleepwalk, and seems somehow telepathically aware of the killer’s activities, being prone to visions when they are taking place. She has also has an astonishing affinity for insects – so powerful that it can inspire a male beetle to start emitting his mating pheromones even though it isn’t his species’ mating season, or a nocturnal swarm of flies.
When Jennifer and the Professor cross paths, he turns out to be the best ally she can find in the area, especially after Jennifer’s roommate Sophie (Federica Mastrolianni) is slain by the killer. The school headmistress (Dalila Di Lazzaro) and the other students hate and fear Jennifer for her abilities, but the Professor sees them as a gift – a gift which might make Jennifer a uniquely capable detective. But this is a Dario Argento movie, so you know the killer’s not going down easily…