It's 2 a.m., a thunderstorm is throwing sheets of rain against the window, and I'm playing Slender with my headphones on.

Every part of this is bad.

I'm that guy in the horror movie. I investigate that strange noise. I ask, "Is someone there?" And worst yet, I'm aware that doing these things is completely stupid.

Developer Mark "AgentParsec" Hadley's terrifying first-person horror game, based on the Internet-born Slender Man mythos, revels in letting you know that you're that person. At the beginning, your character climbs over a fence to enter a creepy, shadowy forest armed only with a flashlight and a handheld camera -- which is to say that she isn't armed at all.

It only gets worse from there.

Your task is simple: Collect eight pages with creepy drawings on them. The pages are on different landmarks throughout the forest, but they appear in slightly different places every time you start up the game.

But the Slender Man is following you, and he gets closer with every page you collect. Slender builds tension with this link between progress and danger; you know that being "good" at the game only increases your odds of darting around a corner to run face-first into the game-ending monster.

Tension exists between jump scares, and the longer that negative space lasts, the riskier it gets for your nerves and unsoiled pants. Slender exists in that space: It wraps it around itself -- and you -- like a thin blanket, useless against the cold. And it makes sure you understand exactly where you are, and why.

And it does this with a black background, some creepy noises, and the idea that the Slender Man is out there. It doesn't have to show him until it's too late -- but it might anyway because that's how it rolls.

That's horror: The knowledge that you are helpless in a situation in which you have no control or defense. The void of the Slender Man's white face is a reflection of the stark blackness of the night, but it is not an opposite. It is the final void, the one that awaits you when your wits or batteries run out and you make that wrong turn or take that wrong step.

It is a blank canvas of futility.

Slender terrifies me, and I'm hooked. You can download it for free from a number of sites if you really feel like putting yourself through all of that.