Plot
Emma Grossman, a nine-year-old girl and daughter of widowed father David Grossman, watches a cat drown in the fountain beneath her bedroom window. At breakfast, she expresses to her father her hope to win a Citizenship medal handed out each year to a student who exemplifies the values of the school.
The "merit day" arrives and Emma is seated in the crowd, certain that she will win the medal. To Emma's shock and disappointment, Mrs. Ellis announces that the winner of this year's medal is Emma's classmate Milo Curtis.
Later, all students and parents are celebrating outside and Emma expresses contempt for Milo to her father, who scolds her for her bitterness. Emma apologizes, but she secretly guides Milo away from the party and through a nearby patch of trees until they reach rocky cliffs overlooking the sea. She slowly moves towards him and murders him off-screen by pushing him off the cliff, after stealing the Citizenship medal from him, then sneaking back to the party. Milo's body is found shortly thereafter by two girls who scream for help. Emma and David watch from a distance as people desperately try to resuscitate him and his mother breaks down into hysterics.
The next day, David asks Emma if she is feeling okay following what happened to Milo, but Emma acts cheerful and neglects to talk about the matter with any kind of empathy. David's sister Angela, a psychiatrist, suggests to David that Emma is in shock and will find time to grieve whenever she is ready. Chloe, a babysitter David hired, begins work. Emma notices her stealing Xanax from David's bedroom, and tells her she knows what Chloe did as they are watching a film. Emma utilizes this fact to manipulate Chloe into doing tasks for her such as getting her ice cream and letting her stay up past her bedtime.
Milo's funeral is held and Emma and David speak with Mr. and Mrs. Curtis. Emma feigns sadness in front of them. Mrs. Curtis asks David for photos that he took of Milo from the day of the ceremony. That night, as David peruses the photos, he notices Emma in the background of many of them looking at Milo and his medal with a contemptuous scowl.
The next day, Mrs. Ellis and an investigator arrive at David's house to ask him questions, and Emma eavesdrops on the conversation. Mrs. Ellis explains that Emma was the last person to be seen with Milo, having been witnessed taking him into the woods. David becomes anxious and assumes they are insinuating something dark. Chloe appears behind Emma in the next room, deducing that Emma killed Milo. In order to prevent the adults from discussing the matter further, Emma smashes a cookie jar and scratches her arm on broken glass, screaming. Mrs. Ellis and the investigator promptly leave. David asks Emma if she knows anything about being out on the rock-face with Milo, but Emma says she was never there with Milo and that Mrs. Ellis is lying because she has always hated her.
Whilst Emma and Chloe are out on a walk the next day, Chloe talks to Emma about what she did to Milo, but Emma denies everything. Chloe and Emma see Mrs. Curtis and the investigator arrive at Milo's house, and Chloe says that Emma had better get her story straight or they could charge her for murdering him. Back at the house, Chloe and Emma are eating together and Chloe lies to Emma, saying that if she gets caught for murdering Milo she will be put into a little electric chair for children that's been painted pink. Emma says she doesn't believe her but appears worried about the notion. Later on, Mrs. Ellis gets into her car; a wasp nest has been put in it by Emma and she crashes offscreen. Chloe discovers Milo's citizenship medal hidden under Emma's bed and hangs it from a lamp in David's room.
When David returns home, he does not notice the medal and Emma soon arrives. She finds the medal hanging from the lamp and secretly takes it off, hiding it behind her back. David asks her what she is hiding and Emma shows him the medal. Distressed, he interrogates her about where she got it and if she was out on the rock face with Milo. Emma admits that she was, but lies, saying they played a game and Milo let her wear the medal for a short time, but when she left the rock face he didn't return, so she kept the medal.
Concerned about Emma's behavior, David calls his sister Angela for the number of a child psychiatrist; he is extremely worried that Emma may have been involved in Milo's death. The next day, David makes Emma return the medal to Mrs. Curtis. That night, he researches antisocial behavior in children and seems convinced that Emma's behavior is psychopathic. The next day, Emma visits a child psychiatrist, and acts normal, deceiving her. The psychiatrist, Dr. March, (named after the author of the novel, The Bad Seed,) assures David that Emma is “one hundred percent normal”.
Later, Chloe goes into Emma's room taunting her, telling her that she wants to hook up with David and that one day she may become Emma's stepmother. Emma is disgusted and says she is going to make sure David gets rid of Chloe. That night, as David is preparing for a date, Emma repeats the conversation she had with Chloe. He assures her that what Chloe said isn't true. Emma says she never wants a stepmother.
Chloe is watching a film downstairs and searches for Emma. Seeing that the work-shed lights are on, she goes and looks inside for Emma. Emma locks her in and sets the shed on fire, killing Chloe. David rushes home but the emergency services have already arrived. He later goes into Emma's room, and she is pretending to be asleep; he questions her about the recent deaths. Emma ultimately admits to murdering Milo, Mrs. Ellis, Chloe, and her previous babysitter whom she didn't like. Emma justifies these murders, claiming she didn't do anything wrong. David is heartbroken.
The next day, David drives Emma to a lake house a few miles away, evading the suspicious Sheriff Peterson. He doesn't want Emma to end up in an institution or in prison and plans to kill her and then himself. Emma senses this, and switches on the gas fireplace as well as the cast iron stoves in the kitchen, attempting to kill David in an explosion.
He wakes up before this happens and brings Emma back to the lake house. He crushes some medicine and puts it into Emma's hot chocolate, but Emma switches the mugs without his noticing. He drinks his and when he is asleep, Emma tries to shoot him with his gun but misses. He chases her and Emma calls 911, screaming for help. The caretaker of the lake house hears the gunshot and arrives with his shotgun to find David about to kill Emma as he claims that Emma is evil. The caretaker shoots David and Emma remains unharmed as the authorities arrive.
The next morning as David's body is being removed, Emma sits solemnly in the back of a car and hugs her aunt Angela, staring into the distance with a cold and victorious grin.
