Plot Summary

Four years after her father David's death, Emma Grossman (Mckenna Grace) is a teenager living with David's sister Angela, her husband Robert, and their infant son Cade. She is still unsuspected for the murders she committed and masks her psychopathy with the facade of a normal teenager whose life consists of school, her friends, and boys. She still commits random acts of cruelty like taking a dog into the woods and killing it as different newspaper articles cover up mysterious deaths.Three weeks ago, Emma prepares for a spot on the school dance team. Emma tries to drown Cade by leaving the back door open so he will crawl into Angela's pool. Angela saves Cade at the last minute, and blames Robert for not keeping a closer eye on the child.When Robert begins to suspect that Emma had something to do with Cade's near-drowning, she tries to kill him by slipping the jack on his car while he works on it, but he survives. As he recovers, she takes sadistic pleasure in ignoring him while he suffers. He threatens to have her institutionalized unless she goes to boarding school and stays out of their lives, so she begins planning to get rid of him.A new girl at school, Kat, infiltrates Emma's circle of friends and says she remembers Emma bullying her in grade school and that she knows about the murders she committed. Meanwhile, Emma's friend Steph is elected captain of her school dance team, a position Emma wanted, so she kills Steph's dog and triggers her epilepsy during class by stealing her medication, resulting in a seizure that kills her.Angela finds video footage of Emma taking Steph's dog and confronts Emma, who admits to taking the dog but insists she did not hurt it. She talks with Brian, the property caretaker who shot David. He tells Angela about David claiming that Emma "would do it again" shortly before he died, although he did not know what that meant. Angela realizes that Emma committed all of the murders and that she has antisocial personality disorder. Emma realizes the same thing after reading the Hare Psychopathy Checklist online, and is thrilled.Emma lures Kat to her house by promising to tell her "everything" and poisons her hot chocolate. She then calls 9-11 claiming that Kat is burning down the house, and sets a fire in the kitchen. Robert hears Cade crying and struggles up the stairs to save him only to find that Emma has left a recording of Cade's cries in his crib. Emma taunts him as she leaves him to die. Angela arrives as the house burns down and calls Emma a monster before rushing inside to save Robert. She is too late and they both die of smoke inhalation. When the police and fire department arrive to fight the fire, Emma is consoled by Nathan.Some time later, a social worker promises to keep her and Cade together in the foster care system. As the social worker goes to make the arrangements, Emma looks out the office window and flashes a cruel victorious smile. (thanks to Wikipedia)