If you watch this as a horror, you'll be disappointed. There are no real jump scares, and the terrific sets for plot terrors are wasted. If you watch this as a moral for bullying, ego, and greed, it's okay.
A girl, Park Song Young, who is what is known as an "outcast" (a cruel position in the "often judgemental" rumor-based Korean hierarchy system) is set up by her "so-called friend", Hye Jin, to do a trending horror (internet) challenge called "Hide-and-Seek," (or One-Man Tag as it's known in Korea).
In the challenge, you drown a doll filled with your hair and salt while you are IT first. After finding the doll where you left it, you stab it while telling it that it is now IT. You hide, and when you return to the doll, you burn the doll, thus ending the game.
However, tired of being an outcast, Hye Jin sabotages the game for her other friends. What follows afterwards is a slew of nightmarish supernatural occurrences that attracts Afreeka's Tv Vjs Glow and Park, skeptical supernatural investigators. Following the money, VJ unwittingly inserts himself in the game, and I suppose this is where the real fun is supposed to begin.