At Università per Stranieri di Perugia, after art professor Franz's lecture on Perugino's painting of St Sebastian, student Jane approaches Franz to discuss the painting. Student Stefano joins the conversation to get closer to Jane's friend Dani, for whom he has unrequited love. Franz parts from the group, and Dani rejects Stefano's advances and rejoins Jane and their friends, including Carol and couple Katia and Ursula. That night, a peeping tom strangles Carol's friend Flo with a red-and-black scarf after slashing Flo's lover's throat.
The next day, Carol sees young doctor Roberto buying a red-and-black scarf from a lecherous street vendor. Carol meets Dani and is distraught to learn of the murders. Jane and Franz agree to attend a concert together. Jane sees Dani's wealthy uncle trying to break off a secret affair with Carol. That night, Stefano pays for a prostitute, whom he assaults for implying that he is homosexual or impotent. Carol attends a party with two men: Peter and George, who are infuriated when she rejects their sexual advances and leaves. She wanders into a swamp where she is murdered by Flo's killer, who had stalked her to the party.
Police inform the students about the scarves used by the killer and implore them to report any information. The killer threatens to murder Dani if she reports who she saw wearing a red-and-black scarf. After escaping another encounter with Stefano, who grabs and kisses Dani without her consent, she remembers seeing Stefano in a red-and-black scarf the day after Flo's murder. Dani's uncle suggests she spend time away at her family's villa in Tagliacozzo. Dani invites Jane, Katia, and Ursula to accompany her there. The killer runs over the street vendor for blackmailing him.
Dani encounters Roberto on the train to Tagliacozzo. After learning that Stefano left his apartment without explanation, Jane drives to the villa and leaves her car to be washed overnight at a service station. The killer spies on Katia and Ursula having sex at the villa. Upon discovering that a local peeping tom is spying on them, the killer murders him.
Stefano spies on the man delivering food to the girls. When Jane sprains her ankle, doctor Roberto gives her a sedative to help her sleep. Later, Dani answers the door, and Stefano's corpse falls to the floor in front of the killer, who murders Dani, Katia, and Ursula.
Jane wakes to the massacre and hides while the killer dismembers and removes her friends' bodies. She attempts to attract attention from townsfolk by signalling with a mirror from the window. The killer locks up the villa and departs, trapping Jane.
That night, the killer returns and is revealed to be Franz, who became a psychopathic misogynist after the childhood trauma of witnessing his brother fall to his death while fetching a girl's doll. He tells Jane that Flo and Carol seduced him into a threesome and blackmailed him, and that he continued his killing spree to eliminate all witnesses. He tries to strangle Jane, but is attacked by Roberto, who saw the flashes from the villa window and learnt that Jane's car was still at the service station. Roberto pursues Franz to a barn and then to the cliffside where Franz falls to his death.
The film was released with its original title in Italy on January 4, 1973.[3] Joseph Brenner Associates later distributed a recut and rescored dubbed version as Torso in the US and the film became a success there on the drive-in and grindhouse circuits, often as a double feature with The Texas Chain Saw Massacre (1974).[5]
George Anderson of the Pittsburgh Post-Gazette deemed the film "another display of softcore sex and seamy violence that might better have been kept abroad."[7] Joe Baltake of the Philadelphia Daily News wrote: "Blood flows freely and limbs detach easily, in Sergio Martino's Torso, a disagreeable Italian import with—not surprisingly—little to recommend it."[8] The Los Angeles Times's Linda Gross wrote that the film was a "lazy suspense movie" with a "disjointed and loose" screenplay.[9]