Final Girls by Mira Grant
This was a short but excellent story.
Takes a potent look at technology/fear and how it could theoretically mix via virtual reality. Grant is a real master at bringing horror scenarios to life and making you care about characters fast.
Fiction and reality become intertwined when horror shows up in the real world. These final girls, the skeptic and the inventor of the technology, are thrust together through technology and may never be the same again.
That ending is what really gets me though and makes it a 5/5 kind of story. You think it's going to have an expected ending and then WAM you get to see the repercussions of it all.