Miguel, a young man with a horribly disfigured face, attempts to trick a girl into sex by putting a mask on and pretending to be her boyfriend. When she unmasks him, he brutally stabs the young woman with a pair of scissors. After the crimes, Miguel is institutionalized at a mental asylum for five years. When his sentence is finished, he is released into the care of his sister, Manuela. Along with their invalid aunt and countess Maria Gonzales, his incestuous sister Manuela operates a boarding school for young women called Europe's International Youth-Club Boarding School of Languages, on the Spanish resort of Costa Del Sol.
When Miguel rides the train ride from the sanitarium, he spots long-haired brunette woman named Angela. Meanwhile, professor Alvaro arrives at the school to visit Manuela, in which Maria states that she is being plotting against and that Manuela only wants money. That night, Maria lies in bed before she is burned to death with a torch. Angela arrives at the school later than her friends, and stays in the room where the girl was killed by Miguel. While wiping the bathroom mirror, she sees Miguel reflected before running outside, where the man follows her. She is then cared by her friend Inga, and the two go to visit Laura, Eva, and the gardener Antonio. Miguel goes to see his sister, and he proclaims his love to Manuela; the two kiss and touch. Manuela stops him, reminding him of the incident years earlier and citing that nobody understands them.
After a night at the disco, Antonio walks Angela home and reads in bed. While the killer sneaks inside the room, Eva appears at her window and asks to borrow a pullover. While Eva changes, the killer attacks and pierces a long knife into her back. Despite the body found Eva and alerts Antonio, the corpse soon disappears. The next day in the Spanish class that Alvaro teaches, the class is listening to tapes of Spanish dialect. On Angela's tape, the voice suddenly changes and threatens to cut her with a hacksaw. She screams when she sees Miguel at the window, but disappears when Alvaro returns and the tape resumes back to its lessons. After finding bloody clothing at Eva's place, Angela sees Antonio arguing with Manuela before a boulder rolls down a hill and nearly kills Angela. While Manuela notices one of her snakes is missing, Angela asks around for Eva, before seeing Antonio killing a snake with garden shears, and runs. While Antonio tries to stop her, Alvaro appears and tells her to stop bothering his students.
Laura and her friends go to Angela's room, where Inga is inside feigning a sexual act inside. While she does not notice the dead Eva hanging in the closet, the girls see Inga through the window and laugh at her. Outside, Angela sees Inga drive back in a yellow car, similar to one Manuela drove. The masked killer takes Inga somewhere, as she has accompanied the person willingly, where she is tied with rope. The killer turns on a saw and pushes Inga towards it. After a young boy turns off the machine, the saw is turned back on and decapitates Inga, before the killer chases and splatters him with the car. Meanwhile, Angela packs in her room, where she sees Antonio at the front door and Miquel at the window, she panics and barricade herself in the room. She then lets Laura inside and offers to stay for the night, where she goes to the disco club to grabs some drinks. When Laura returns, the killer strangles her with thongs around her neck. Angela, after receiving a threatening phone call, finds the dead bodies of her friends and is attacked by the killer. While Miquel is knocked out during the struggle, the girls sees Alvaro driving off in his car. Angela runs to Manuela and tells her about the bodies. Manuela takes her to a room and gives her a drink to relax her.
Manuela and Alvaro discuss the killings that he has done, and an awakened Miguel hears them talk of blaming the murders on him. Manuela also talks of how Miguel thinks she loves him, and mentions his disfigurement. She tells Alvaro that she has already been paid and tells him to kill Angela. Miguel goes to a room and, eventually believing that Angela is his sister, chokes the blonde until she shoves a spike into his neck. Angela runs downstairs and sees Alvaro and Manuela struggling, before screaming at the body of the countess Maria found inside a room. Alvaro runs into the room and holds a knife to Angela, but Manuela appears and murders Alvaro with a power saw; she puts the saw to Angela's throat and reminds her that she saved her life, where Angela nods and runs away. Manuela then goes to her room and talks to her dead brother, but Miguel sits up and strangles Manuela. The film ends with Miguel collapsing and holding onto his sister's hand, while Antonio embraces with Angela as the police arrive.
To whom does Miguel confess his love?
Manuela