On May 31, 2014, in Waukesha, Wisconsin, a twelve-year-old girl was found lying on a trail, bleeding from nineteen stab wounds. She told the cyclist who discovered her that her two best friends had lured her into the woods and attacked her. When asked why, the girls gave an explanation that seemed impossible: they said they had done it for Slenderman—a fictional character created on an internet forum years earlier. This is the story of Morgan Geyser and Anissa Weier, two children who became convinced that a creepypasta legend was real. It's the story of how online fiction can blur into belief, how untreated mental illness can fester in silence, and how a friendship built on shared delusions can lead to unthinkable violence. What happened in the woods that morning would raise questions nobody could adequately answer—about where childhood ends and psychosis begins, about culpability and justice, and about what happens when the internet's darkest corners reach into the lives of vulnerable children.

Officer Roland was ready to clock out for the day. Fortunately the police station barely had much excitement, so there wasn’t much reports coming in at the front desk. This meant, he can finish up his...