A link to a video reaches high school senior Julie through her preferred social networking app, INSTATOCK. In it, her friend Albert appears to be brutally murdered. Julie and her friends, a tight clique of privileged high schoolers, aren't sure if it's a practical joke until news arrives that a victim of Albert's bullying pranks has escaped from a mental hospital. Only as the group's numbers dwindle do they realize someone is using their posts on the app to stalk them.