HBO has a boogeyman story for you… except this one is all too real.

The upcoming true-crime documentary Beware the Slenderman (premiering Jan. 23) tells the tale of the notorious 2014 stabbing of a 12-year-old Wisconsin girl by two of her classmates. The accused girls told authorities they did it to appease the Slender Man, a fictional ghoul taken from a popular horror-story collective online.

The trailer, which you can watch above, starts with American Horror Story-esque black-and-white footage of the Slender Man — a very tall, pale, faceless creature with tentacles on his back — with a young girl in the woods while a voice reads a disturbing nursery rhyme: “The palest man/The blackest suit/Quicker than the tallest brute.” Then we learn the real story, with one accused girl telling the cops that “he said he’d kill our families.”

The case becomes a media sensation, and a lesson on the thin line between fantasy and reality. As one boy who’s interviewed puts it: “To believe in the boogeyman isn’t that hard… and they believed it was real.”

Will you watch HBO’s Beware the Slenderman? Or was the trailer creepy enough?