As the camera glides through a domestic environment, the jarring sounds of raised voices slice through the calm, their shadows being the only harbinger of their real presence. In the midst of this turmoil, a teenage girl, Matthea Lára Pedersen, unexpectedly reacts to a bone-chilling bird call echoing through the area. Her abrupt escape into the woods coincides with a phone call between two men, one informing the other that their upcoming subjects will be easier to control.
In a secluded area of the Bavarian Alps, teenage Gretchen, played by Hunter Schafer, strives to adapt back into family life following the death of her mother. She now lives with her father, Luis (portrayed by Marton Csokas), and his new wife, Beth (brought to life by Jessica Henwick), all while surrounded by breathtaking alpine scenery. The complexities of Gretchen's life are further heightened by the presence of her mute half-sister, Alma (expressed by Mila Lieu), whom Gretchen insists on regarding merely as "her father's daughter." Their family eventually meets Dr. König (played by Dan Stevens), a mysterious figure associated with the hotel where Gretchen has found work.
Embarking on her new role at the hotel alongside Dr. Bonomo (characterized by Proschat Madani), Gretchen is required to spend time with Alma. Their relationship takes a quirky turn as they engage in a musical interplay, with Alma attempting to imitate Gretchen's air-guitar antics. However, the eerie bird call reemerges, triggering a seizure in Alma and forcing Gretchen to relive a haunting sequence until Alma inflicts a scratch on her own face. Just as the noise fades, Luis and Beth arrive to care for their daughter.
Gretchen's experiences at the hotel blur the borders of reality and enigma. She develops a unique friendship with Trixie (played by Greta Fernández), a fellow music enthusiast. Their bond contrasts with Gretchen's observations of an unidentified woman who is seen repeatedly vomiting in the lobby, tended to by her spouse before Gretchen encounters Ed (portrayed by Astrid Bergès-Frisbey), a guest seeking both a room and a six-pack of beer. The same unknown woman appears later in another instance, vomiting once more before consuming something and fading into obscurity.
As twilight approaches, Gretchen sets out on a solo bike ride home, defying König's cautions about traversing the perilous woods after dark. The night seems alive as she navigates through shadows, unaware of the disturbing figure - the Hooded Woman (played by Kalin Morrow) - that stalks her. Her desperate attempt to seek help at a nearby station results in pandemonium when she accidentally slams into a glass door, causing an agonizing gash. The hooded figure vanishes as mysteriously as she emerged, leaving a lingering tension and a brazen police report dismissed by Erik.
The following day, Gretchen encounters Henry (played by Jan Bluthardt), a veteran detective investigating a series of horrific murders linked to the same hooded figure from the previous night. His captivating words draw Gretchen deeper into a world shrouded in darkness and deceit.
As Gretchen finds herself ensnared in a time loop, she relives cherished memories with Ed, sharing a forbidden kiss underneath the stars. Suddenly, their magical evening is interrupted by the Hooded Woman, who triggers a devastating car crash that sends Ed hurtling away. Gretchen awakens back at the resort, met with the somber expressions of her father and Beth. Henry resurfaces, haunted by recollections of his wife's tragic fate.
Teaming up with Henry, Gretchen begins to surveil the Lovers Lounge, where the latest victims - Trixie and Erik - are expected to indulge in a romantic evening together. However, just when peace seems achievable, the chilling bird call echoes through the air again, rekindling their fears as the Hooded Woman makes her presence known. She terrifies Trixie before knocking her unconscious. Gretchen and Henry rush to save their friend, rolling her onto her side to prevent a tragic end.
As the dark mystery unfolds, Gretchen finds herself woven into a tangled web of deceit, homicide, and manipulation. The true intentions of the Hooded Woman loom ominously, but it becomes evident that Gretchen must navigate this treacherous maze with utmost care to ensure her survival through this perilous night.
Confronted with her father, Luis, the next morning, Gretchen's pent-up anger erupts in an intense confrontation over the sinister occurrences at the resort and König's shadowy role in them. König then reveals a package that has arrived at their doorstep, sending Gretchen into a tailspin when she discovers it contains all her mother's possessions, which were supposed to be lost to time. Luis' reluctant admission that he sold their childhood home only ignites Gretchen's fury further as she grapples with this betrayal alongside the cherished memories of their past. Observing from the window, König plays a haunting melody on his flute, conjuring the eerie call of a screeching bird that resonates like an ominous warning through the space.
With tears streaming down her face, Gretchen retreats to her room in search of comfort, finding solace in the melancholic echoes of her mother's voicemail messages. Once reminders of Alma's love and presence, they now painfully highlight their irreplaceable loss. Just then, a cryptic message seemingly delivered by text-to-speech technology beckons her, an invitation from her mother, no doubt manipulated by the Hooded Woman.
While her family seemingly disappears into thin air, Gretchen uncovers a distressing revelation: Alma has suffered a seizure and is taken to the hospital. König offers his hollow condolences, his eyes gleaming with a calculating coldness. While he misguidedly directs Gretchen toward the nearest train station, she unwittingly finds herself ensnared in a devious trap, led straight to his sinister lair where Erik holds Henry captive.
The shocking realization washes over Gretchen: Henry, once a trustworthy detective, has been dismissed from his position following his inquiries into König's corrupt activities. As König begins to spray her with pheromones and imprison her in the pool house, her desperate cries go unheeded. Just as she attempts to make her escape, the same enigmatic teenage girl from earlier thwarts her efforts once again.
König returns, exuding an air of malevolence as he divulges the true nature of his twisted scheme: the Hooded Woman belongs to an ancient inhuman species known for impregnating human women with their offspring, enabling them to be raised by humans until they're mature enough to reunite with their kind. Ultimately, Alma is revealed to be a product of such an unnatural union, her existence merely collateral in the Hooded Woman's chilling plans.
In a fervent attempt to reclaim her agency, Gretchen makes a bold effort to break free only to find herself once more ensnared in the time loop. The piercing cry of the bird taunts her, mocking her struggles to elude König's clutches. Just as the situation seems dire, Henry swoops in, displaying his resourcefulness and courage, striking down both König and the teenage Cuckoo with precision. As the dust settles, Gretchen finally tastes freedom, yet her ordeal is far from over, her fierce resolve to resist the encroaching darkness burning brighter than ever.
Rushing toward the hospital, Gretchen and Henry are engulfed in a heavy sense of dread. Dr. Bonomo, usually composed, stands ready to spearhead an experiment aimed at reconnecting Alma with her primary Cuckoo mother, the ominous Hooded Woman. Simultaneously, Beth's sudden decline prompts Luis to take her away for urgent care. Amid this pandemonium, König miraculously recuperates from his gunshot wound and exacts a brutal personal vendetta against Bonomo and her assistant. Anguished, Henry believes Alma is a monstrous being deserving of eradication and restrains Gretchen from intervening during this chaos.
Ultimately, Gretchen's desperation boils over as she plunges her butterfly knife into Henry, breaking free to rescue her sister. Their heartfelt reunion is abruptly interrupted when the Cuckoo mother emerges, relentlessly pursuing Gretchen. The creature stalks her through the convoluted records room, its predatory gaze fixated on its quarry. As Henry limps in to help, his clumsiness sets off a catastrophic chain reaction, causing shelves to topple. In the throes of confrontation, Gretchen lands a decisive blow, quelling the creature's reign of terror.
In the aftermath of the chaos, Alma narrowly evades capture as Henry and König engage in a deadly pursuit. Gretchen's courageous act rejuvenates her sister, allowing her to reconnect with the cherished message from their shared past: "thank you." Together, the sisters make a desperate rush for liberation, as they are relentlessly chased by their adversaries.
As they escape the facility, both König and Henry meet their gruesome end in a hail of bullets. Stepping into the sunlight, the sisters discover Ed waiting for them outside the hospital, her presence delivering a glimmer of hope. With Ed behind the wheel, they speed away from the desolate memories of the resort, embarking on a new chapter in their tumultuous journey.
