One night, while teenagers Blaire, Mitch, Jess, Adam Ken and Val take part in an online group chat session, they are suddenly joined by a user known only as "Billie227." Thinking it's just a technical glitch, the friends carry on their conversation... until Blaire begins receiving messages from someone claiming to be Laura Barns, a classmate who killed herself exactly one year prior. As Blaire tries to expose Billie's identity, her friends are forced to confront their darkest secrets and lies.