After the death of her mother, grief-stricken teenager Gretchen moves with her father Luis, stepmother Beth, and mute half-sister Alma to a resort town in the
Bavarian Alps. The family is there to help build a new hotel, overseen by the enigmatic Herr König, who offers Gretchen a job at the front desk to help her adjust. Soon after their arrival, strange things begin to happen. Gretchen encounters multiple female guests vomiting, Alma suffers seizures triggered by a mysterious reverberating shriek, and Gretchen has a terrifying encounter with a hooded woman while biking home one night, but the incident is dismissed by police as a prank. Gretchen meets a detective named Henry who is investigating a murder linked to the hooded woman. She also becomes close to a female guest named Ed, and the two plan to run away together. However, their escape attempt is thwarted when they hear the disorienting shriek, nearly run over the hooded woman, and crash their car, leaving Gretchen severely injured and confined to the resort as Ed recovers in the hospital. Henry explains to Gretchen that he believes the hooded woman is responsible for at least one murder, which ended in the female victim choking on her own vomit. He believes that one of the vomiting women whom Gretchen saw earlier may be connected. She and Henry stake out a cottage, where the hooded woman attacks Gretchen's coworker, Trixie, in an attempt to implant her with a mysterious slime. The next day, Gretchen confronts Luis and König, expressing her disapproval of their involvement in the resort. During the argument, König accidentally reveals a package addressed to the family containing items belonging to Gretchen's mother. Luis confesses that he sold their old family home. Enraged, Gretchen retreats to her room and listens to her mother's old voicemails. Among them, she hears a voicemail from Alma, using
text-to-speech, imploring Gretchen's mother to contact Gretchen to make her happy. Gretchen emerges from her room to find her family missing. König tells her that Alma had another seizure, and they took her to the hospital. He says that he will take her to the nearest train station so she can run away, but first, they will drive to his house so he can give her some money. There, König reveals the truth: Henry is a disgraced police officer, and the hooded woman is not human but a member of a near-human species that relies on
brood parasitism, much like
cuckoo birds. These cuckoos use their shrieks to disorient humans and trigger the development of their young. The cuckoos' young, like Alma, are implanted within human surrogates, and raised until they are ready to join their true kind. König has been experimenting with preserving this species at the resort, where Beth and Luis unwittingly stayed during their honeymoon years ago. König locks Gretchen in a pool house and uses a flute to summon a teenage specimen of the species. The adolescent cuckoo is drawn to Gretchen and attempts to inseminate her using slime. However, Henry arrives just in time, shooting König and killing the creature. Henry and Gretchen race to the hospital, where König had prepared to reunite Alma with her true mother, the hooded woman. Gretchen realizes that Henry intends to kill not only the adult cuckoo but Alma as well. Desperate to save her sister, Gretchen stabs Henry with her butterfly knife. Gretchen reaches Alma and keeps the mother at bay by feigning a threat to stab Alma. Alma misunderstands and flees. Giving chase, Gretchen is pursued by the mother. Gretchen uses a pair of headphones to muffle the mother's screeching and stabs the mother in the throat, killing her. Gretchen reunites with Alma, regaining her trust by thanking her for her message to her mother. They find the still-alive König and the injured Henry in a standoff. Seeing both of the men threatening them with guns, Alma covers Gretchen's ears and lets out a powerful shriek, disorienting both men long enough for the sisters to escape. Henry and König shoot each other dead. Outside, the sisters are met by a recovering Ed, who drives the girls to safety, and the three flee the resort. ==Cast==