Orphan first kill

On January 26, 2007, Estonian psychiatric patient Leena Klammer, a 31-year-old woman with a rare hormonal disorder called hypopituitarism that gives her the appearance of a 10-year-old child, orchestrates an escape from the Saarne Institute by seducing and killing a guard and hiding in the car of Anna, an art therapist. After breaking into Anna's house and killing her, Leena looks up missing American girls and finds that she bears resemblance to a girl named Esther Albright, who went missing in 2003. Later, posing as a lost girl, Leena is approached by a Russian police officer and introduces herself as "Esther", claiming that her parents are in the United States.

In Darien, Connecticut, wealthy artist Allen Albright and his wife, philanthropist Tricia, who has since come to terms with the disappearance of their daughter, are informed by Detective Donnan that "Esther" has been found. Tricia travels to the U.S. embassy in Moscow where she is reunited with Esther. Tricia brings Esther home and immediately starts to have doubts when she notices that Esther has forgotten about the death of her grandmother or that her painting skills have increased enormously compared to before she disappeared. Leena grows fond of Allen after they both start bonding over their painting skills, and tries to separate him from Tricia.

While Tricia and Allen attend a charity gala hosted by Tricia, Donnan arrives at the house and steals a vinyl record from Esther's room which has Leena's fingerprints on it. He takes it back to his house, unaware that Leena has followed him, and analyzes the fingerprints to find it is not a match. Leena attacks Donnan before Tricia arrives, having followed Leena, and shoots him dead. Tricia reveals that she knows Leena is not Esther, who died four years earlier during an altercation with Tricia's son Gunnar, which Tricia covered up without Allen's knowledge. Leena reveals her true identity to Tricia, and the two then dispose of Donnan's body in a cellar hatch where Esther was buried and frame his disappearance as a vacation trip by forging an email to the police station. 

Knowing that it would be too suspicious if "Esther" were to disappear again, Tricia agrees to continue Leena's act for Allen's sake, and Leena and Tricia remain on guard with each other. Tricia eventually attempts to poison Leena during dinner, but Leena refuses to eat the food and excuses herself. Leena feeds the food to the rat that lives in her room and later finds the rodent dead from ingesting the poisoned meal. Leena retaliates by making a green smoothie mixed with the rodent's carcass for Tricia. Allen reveals he is going into the city to meet about a potential art gallery. At the train station, Leena attempts to kill Tricia and Gunnar by pushing them in front of a train, but her attempts are interrupted by a passing commuter. With Allen away, Leena tries fleeing by stealing Tricia's car, but she is soon found by a police officer.

That night, Leena is brought back to the Albright house and Tricia and Gunnar finally decide to kill Leena. Tricia tries to stage a suicide, but Leena fights back and flees before Gunnar throws her down the stairs. Distracted by a phone call from Allen, who is returning home, Tricia and Gunnar search for her when she disappears. Leena shoots Gunnar with a crossbow, then repeatedly stabs him with his fencing sword. Tricia and Leena fight in the kitchen, inadvertently setting the house alight in the process and the pair flee to the roof as Allen returns home.

Tricia and Leena both slip and end up clinging to the roof, begging Allen to save them, with Leena claiming Tricia attacked her, and Tricia trying to reveal the truth about Leena. Tricia loses her grip and falls to her death and Allen lifts Leena to the roof. Allen checks Leena's face, which causes her fake teeth to come free. Realizing she is not Esther, Allen calls her a "monster". Leena tries to defend herself saying "she did it for them" and that she "loves Allen". Enraged, he falls off the roof to his death. Leena then dresses herself up as "Esther" and leaves the burning house after cleaning off the blood on her face. Later, "Esther" is moved to an orphanage where she waits for a new family to adopt her