It was a local story that horrified the nation: two 12-year-old girls lured a friend into the Waukesha woods, where they proceeded to stab her 19 times in an effort to appease a faceless mythical entity known online as 'Slenderman.' But there's more to the story than the dark headlines it generated. A sobering documentary that delves deep into the story behind this shocking crime, this film examines how an Internet urban myth could take root in impressionable young minds, leading to an unspeakable act.