When a teen is bullied online by an anonymous classmate and starts losing control of her life, her mom fights to find the truth before her daughter becomes the bully’s latest fatality.

Jenny starts a new high school in the city. Tony offers his friendship, but Jenny is drawn to Camryn, a popular girl. They become best friends. After having no interest in social media, Jenny is convinced by Camryn to sign up for a facebook account and talks her parents into buying her a phone. Jenny likes being able to talk with Camryn and Tony online, but someone else wants to speak to her as well, someone by the name Cutegirl. She sends Jenny bullying messages that interrupt her life.

Jenny’s mom Nancy notices drastic changes in Jenny’s behavior as she becomes more withdrawn and hateful. Her grades already crash when school has just begun, but Jenny refuses to tell her what’s going on. After a girl from school dies in what appears to be an accident, Jenny finds notes in her locker saying to stay away from Camryn. The sender, Sarah, begs Jenny to meet her after school, but when Sarah arrives at the secluded location first, she is killed by a cloaked assailant and dragged away. Jenny assumes she must have changed her mind and left, but starts to worry when Sarah doesn’t come to school the next day.

Nancy finds Jenny’s facebook password in her room and checks her social media page. She sees the discussions between Jenny and Cutegirl, and grows alarmed. The newest one demands that Jenny meet her in the middle of the night to talk things out. Nancy turns off Jenny’a alarm and goes in her place, becoming locked in a barn when the bully mistakes her for Jenny. Nancy escapes and confronts Jenny about her recklessness. All Jenny wants is to be left alone and work things out for herself.

The bully pushes Jenny to do things against her will, such as steal a wallet for her and snatch her mom’s wedding ring. When Jenny brings the ring to a designated drop-off point, she discovers Camryn’s prior best friend Renee is the one who picks it up. Camryn blows it off as jealousy over her having a new friend and vows to get the ring back, but the killer causes Renee to have a fatal accident to silence her.

Jenny discovers that Camryn had been working with Renee as part of a game. When Jenny tells everyone at school what Camryn has done, Camryn posts a fake picture of her topless body with Jenny’s head on social media. With everyone laughing at her, Jenny flees. Nancy learns about it from the principal and goes on a hunt for her daughter, finding Jenny about to jump to her death on a cliff. Nancy convinces her daughter to help her fight against Camryn and together, they devise a plan.

Jenny lures Camryn to an abandoned factory to discuss their situation while Nancy secretly films Camryn’s confession. Camryn learn what they have done and accidentally stabs Nancy as she tries to protect Jenny. Jenny flees inside the building, but Camryn traps her, ready to kill the only witness against her until Nancy arrives and causes Camryn to fall to her death. Back at school, fellow students now admire Jenny for taking a disliked Camryn down. Her true best friend, Tony, is ready to be there for her, as he always has been.