A lost traveler, Vera Grandt (Fiore Argento), meets a gruesome fate when she is found beheaded in the picturesque Swiss countryside. The chilling discovery is made by Inspector Rudolf Geiger (Patrick Bauchau) alongside his assistant, Kurt, who take the remains to entomologist John McGregor (Donald Pleasence). Using maggot analysis, he estimates the time of Vera's death, setting the stage for a dark mystery.
Meanwhile, the story shifts to Jennifer Corvino (Jennifer Connelly), an insect enthusiast attending the Richard Wagner Academy for Girls, under the watchful eye of Frau Brückner (Daria Nicolodi). Her experience begins to take a terrifying turn when sleepwalking leads her to witness a brutal murder. Startled and bewildered, she wakes up and finds herself lost in the shadowy woods. Luckily, she is rescued by Inga, McGregor’s loyal chimpanzee assistant. McGregor comes to suspect that Jennifer possesses a rare gift for telepathy.
As Jennifer tries to piece together her fragmented memories of the murder, a brain scan by the school doctor fails to provide clarity regarding her sleepwalking episodes. The terror escalates when her classmate, Sophie (Federica Mastroianni), is found dead. A mystical firefly unexpectedly leads Jennifer to uncover a maggot-infested glove that holds vital clues about the murders plaguing the academy. However, when fellow students mock her fascination with insects, she retaliates by summoning a swarm of flies that engulfs the entire school, much to their horror.
In a desperate bid to catch the killer, McGregor provides Jennifer with a specimen of the Great Sarcophagus fly, which is drawn to decaying flesh. This leads her to an abandoned house, the site of Vera Grandt's horrific attack. Tragedy strikes again when McGregor becomes the next victim in the series of killings. Devastated, Jennifer decides to leave the school and seeks refuge at Frau Brückner's house. Here, she uncovers Brückner's sinister intentions when she discovers she has been poisoned, leading to a tense escape.
Trapped in a room, Jennifer discovers a hidden tunnel that leads to a grim dungeon where she unexpectedly finds Inspector Geiger, who has been chained up and disfigured. Driven by terror, she escapes his ghastly appearance only to plunge into a pool of decaying bodies, guided by Geiger's desperate pleas. Together, they flee the horrific scene.
The climax escalates as Jennifer encounters Brückner's deformed son, Patua (portrayed by Davide Marotta), who relentlessly pursues her. Using her unique ability, she summons a swarm of flies to fend him off, leaving him to drown in the lake. However, salvation is fleeting as she’s confronted by her father’s assistant, Morris Shapiro (Mario Donatone), who arrives to aid her and is shockingly decapitated by the deranged Frau Brückner.
In a climactic showdown, Jennifer faces off against Brückner, who is dramatically dispatched by Inga wielding a straight razor, bringing this macabre tale to a chilling conclusion. The harrowing events leave one pondering the true horror lurking beneath the seemingly serene surface of the academy.
