Twelve-year-old Tinja practices gymnastics, pressured by her image-obsessed mother, a former figure skater turned
influencer. When a crow flies into the family house, her mother snaps the bird's neck and instructs her to dispose of it outside. That night, Tinja discovers the dying crow in the nearby woods and
euthanises it with a stone. She brings the orphaned egg home and incubates it, hiding it from her family as it grows abnormally big. Tinja meets a new neighbour, a girl named Reetta, and her
French Bulldog Roosa. Returning home one day from gym practice, Tinja discovers Mother is having an affair with her handyman, Tero. Reetta joins Tinja at the next practice session, proving to be very talented. Seeing this, Mother pressures Tinja into practicing until her hand is blistered and bleeding. The egg eventually hatches into a bizarre, human-sized, bird-like creature. It escapes but returns the next evening, injured by a shard of glass. She names the creature Alli, cares for it and lets it sleep underneath her bed. While sleeping, Tinja becomes annoyed by Roosa's barking. She awakens to find Alli on top of her with the dog's decapitated corpse beside her. When this makes her vomit,
Alli eats it. Tinja buries Roosa in the backyard, unaware that her younger brother, Matias, is watching. One evening, when Mother gives Tinja a hairbrush while neglecting Matias, he spitefully digs up Roosa's corpse. Later, when she is downstairs, he wears a mask and sneaks into her room to discover what is under her bed. Alli slashes his mask in fear. Tinja suffers a seizure, indicating that she and Alli are
psychically linked. The next day, Mother is displeased when Reetta wins the competition spot. Alli brutally attacks Reetta on her way home, while Tinja has another seizure. Tinja finds Alli's molted beak and realises the creature is beginning to look more like her. Later, Tinja brings Reetta flowers, horrified by the severity of her injuries and amputated left hand. Tinja returns home and punishes Alli by slapping herself; Alli comforts Tinja while she cries. In the morning, Alli looks fully human except for the pupils. Since Reetta is hospitalised, Tinja is given her spot in the competition. Mother suggests she and Tinja stay with Tero for the weekend; Father implies that he knows about Tero. At Tero's, Tinja learns that he is a widower with an infant daughter named Helmi. Tero is sympathetic to Tinja, deducing she is not truly passionate about gymnastics. Later, when Tinja is feeding Alli, Tero interferes and the creature attacks him, injuring his hand. Despite this, he forgives Tinja and covers for her. Mother arrives to take Tinja to the competition. When Mother fusses over Helmi and makes Tinja jealous, Tinja becomes fearful that Alli might attack Tero and Helmi while she is gone. As Tinja begins her routine, she mentally sees Alli, who is about to attack Helmi with an axe. Tinja sabotages herself and falls, injuring her wrist, which stops Alli. After the competition, Tero, who witnessed Alli's attempted attack, throws out Tinja and her mother, saying that Tinja has serious problems. Before they leave, Mother angrily blames Tinja for ruining her happiness. At home, Mother finds Alli in Tinja's room and, mistaking the creature for Tinja, forcibly brushes her hair, injuring Alli in the process. Alli attacks Mother, but Tinja intervenes and Alli flees, screaming as the sides of its jaw rip open. Tinja explains that all the recent chaos is because of Alli, and they hunt down the creature. In Tinja's room, Alli overpowers Mother, who stabs it in the leg, also injuring Tinja. Tinja tries to explain that she hatched it, but Mother attacks again anyway, only to realise she has instead stabbed Tinja, who has jumped in front of Alli to protect her. Tinja collapses onto Alli and dies, her blood falling into the creature's mouth and completing its transformation. Alli, now looking exactly like Tinja, pushes Tinja's corpse aside. It utters the word "Mother" and stands up, looking down at her. ==Cast==