IN MY DAY, it took a week to get photographic evidence back from a high school kegger. And even then, we were lucky if we could tell who, exactly, was puking their guts out. (We also wore onions on our belts, which was the style at the time.) In retrospect, we didn't know how good we had it. Nowadays, teen suicides because of cyberbullying are not uncommon, and crystal-clear documentation of kids' drunken shame lives forever on the internet. I'd take the onion belts any day.

That's where Unfriended throws its hat into the horror movie ring: The entire film plays out on the computer screen of high schooler Blaire (Shelley Hennig)—through messages, Facebook, Instagram, and email. She simultaneously messages her boyfriend, Mitch (Moses Jacob Storm), listens to Spotify, and rewatches the embarrassing video that drove her friend Laura to kill herself exactly one year ago this very day. On this anniversary, Blaire and her friends gather on Skype and discover a stranger lurking on their group chat. This non-avatared rando has hacked Laura's identity and is hell-bent on avenging the dead girl's suicide in ever-ratcheting machinations.

Unfriended takes place entirely on Blaire's screen, and if watching a teenager toggle around the internet sounds like hell incarnate, well... I'm not going to argue too vigorously. Yet all those open windows and pop-up messages combine to create a compounding edginess, a feeling not unlike being stressed out at work laboring in the computer mines—with the heightened stake of a murderous cyber ghost to add to the flop sweat. It's a tightly contained film that builds until every compromised video feed and ping make you prickle with fright. Two years from now, it'll probably seem outlandishly outdated, like The Net meets The Blair (Blaire?) Witch Project. But for now, Unfriended is a fresh and timely horror flick full of economical scares—things that used to be found via serial-killer rampages in the woods, and now can play out on the webcams of cyberbullies.