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, but is this just his latest practical joke? Julie and her friends, a tight clique of privileged high schoolers, aren’t sure 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 to the app to stalk them, and the small town’s low-tech authorities fail to get ahead of the murders. The tight knit group of friends implodes as the secrets they’ve kept from each other - infidelity, drug abuse, and other betrayals - reveal that the lifestyles they post to social media have little to do with who they really are. However, despite not really knowing each other, InstaTock clearly knows them.