On May 31, 2014, in Waukesha, Wisconsin, two twelve-year-old girls attempted to stab their classmate to death. Their violence was extreme but what seemed even more frightening was that they committed their crime under the influence of a figure born by the internet: the so-called “Slenderman.” Yet the even more urgent aspect of the story, that the children involved suffered from undiagnosed mental illnesses, often went overlooked in coverage of the case. This is the full story told for the first time in deeply researched detail, using court transcripts, police reports, and exclusive interviews. Both a page-turning true crime story and search for justice, Slenderman examines the failures of the American judicial system, the trials of adolescence, and the power of the internet.