White-skinned tall man with spindly arms and legs: that's how Slenderman is described. He is the popular online "creepypasta" that was turned into an urban legend in 2009. But, more than just an online horror story, Slenderman has turned into a real nightmare in the human world, and that is what "Beware the Slenderman" is all about.

"Beware the Slenderman" is an HBO documentary directed by Irene Taylor Brodsky. The story surrounds three girls and their families and the online legend, Slenderman.

The story featured in "Beware the Slenderman" happened in late spring of 2014. Three middle-school girls went into the woods of Waukesha, Wisconsin. But only two of them walked out; unharmed and without any sign of physical injuries.

However, a 911 call led the police to the third girl, found stabbed and dying beside the road. Apparently, the girl had been stabbed 19 times, according to ScreenerTV. She crawled her way to the side of the road to ask for help. She had barely survived.

The following days and weeks have been emotional and chaotic. However, what was disturbing was how they found out that the true suspects of the crime were the child's best friends -- the two girls who went into the woods with her. According to these children, they did the terrifying deed to appease a creature called Slenderman.

It appears that the children had made a sacrifice that they thought would keep their families alive from the Slenderman. They also believed they could live in a place called Slender Mansion somewhere in the woods.

But, as reviews say, the "Beware the Slenderman" HBO documentary does not focus on the memes and the creepypastas involved in the creation of Slenderman. The documentary also does not dive into the guilt of the children, but merely on the psychological and social factors that were really behind the stabbing.

As The Atlantic puts it, "Beware the Slenderman" did not give any simple answers. However, the documentary was able to connect the girls, Slenderman, psychological issues and, most of all, the social factors that gave birth to a crime. "Beware the Slenderman" aired on HBO in January 23, 2017.