| Director | Tara Subkoff |
|---|---|
| Budget | $1.5 million |
Harry Cox is having sex in his car with his mistress, Lisa. After Lisa exits the car, his wife Alex calls him and chastises him on the phone. After he hangs up, his throat is slashed, and Lisa is also murdered.
Twelve-year-old Sam is invited to a sleepover at classmate Sofia Cox's mansion in rural Connecticut. Sam finds herself embarrassed by her lack of wealth amongst her rich and privileged classmates. Also at the sleepover are Francesca, Ava, and Georgie. Another girl, Cat White, is being driven to the house by her father, Dr. White; it is established that Cat is suffering from psychological problems and has been in trouble for bullying the girls.
The girls engage in a pretend fashion show, incessantly posting photos of themselves on social media with their smartphones. Cat arrives, and Alex allows the girls into her walk-in safe where numerous pieces of jewelry and clothing are stored. She then leaves to go into town for a twelve-step meeting.
As the night goes on, the girls, each consumed by their cell phones, begin to fight with one another. Cat instigates a confrontation and taunts Georgie about her weight, and Sofia forces her to leave. Cat storms into the woods, where she attempts to call her father to pick her up. She begins tagging Georgie in a stream of cruel photos on Facebook; the girls collectively decide to lock their cell phones in the safe to avoid Cat's cyberbullying, and Sofia throws the keys to the safe in the house's swimming pool.
After Dr. White receives a frantic voicemail from Cat, he returns to the house and interrogates the girls about his daughter's whereabouts, Ava also runs away from the house after Dr. White scares the girls. He tells the girls he is going to press charges. Sam goes to search for Cat in the woods and finds Sofia's father's car parked, with blood across the windshield. She returns to the house panicked, but the girls do not believe her.
Georgie and Francesca begin to taunt Sofia about her mother's alleged affair with Dr. White, and she leaves. In the woods, Sofia also stumbles upon her father's car and finds his corpse inside. She calls her mother; Alex answers, believing it to be her husband, angrily lashing out into the phone about his cheating, and hangs up. Sofia takes a revolver from the car and flees. At the house, Sam stumbles upon Ava's dead body and is attacked by a masked assailant. She goes to retrieve the safe key from the pool to get the girls' cell phones back.
Georgie has her throat slashed; Francesca is also stabbed to death. Both of their deaths are streamed on the internet, and photos of their bodies are posted online. Sam retrieves the key and opens the safe, but is attacked again, and locks herself inside. On her phone, she finds photos and videos of her friends' murders posted on a social media game by Cat. Dr. White returns to the house and finds Georgie's body. Sam tells him that Cat has killed Ava and Georgie; Cat emerges and unmasks herself. Believing that Dr. White murdered her father, Sofia shoots him to death.
Witnessing this, Cat flees; Sofia then learns that Cat is the murderer. Sam leaves the house to get help. She encounters Cat on the road, wearing the mask. Alex arrives and witnesses Cat shoot herself in the mouth, killing herself. The film ends with a montage of photos of the murders followed by a video uploaded by Cat, which eventually goes viral and she professes her revenge against the girls, saying that she will "be remembered forever."