Oculus, the horror movie about an evil mirror starring Doctor Who's Karen Gillan, has been getting rave reviews since it hit some festivals last year. And now, here's a trailer that shows why that is, along with explaining a lot more of the movie's plot. Warning: trailer is spoilery!

The first trailer for Oculus, which came out a couple months ago, was pretty bare-bones — just some whispering over images of the scary mirror, plus a few quick cuts that give a hint of the craziness to come. But this trailer, by contrast, explains pretty much the whole plot and gives a good look at what appears to be the final twist of the film.

In Oculus, Karen Gillan and Brendon Thwaites are a Kaylie and Tim Russell, whose mother died 10 years ago — and Tim was blamed, so he's spent the last 10 years in a psychiatric facility. But Kaylie believes that a cursed mirror actually killed their mother (played by Katee Sackhoff) and she's determined to prove it, and kill the evil that lives inside it. Unfortunately, it looks as though the mirror has a way of controlling what people see and using false visions to manipulate you. Which is a clever use of our fear of mirrors and illusions.

You gotta love a horror movie where the main characters are actively seeking to fight the evil rather than running away from it — that helped make The Conjuring stand out last year — and horror usually works best when it's a personal story rather than just a random series of terrible incidents. So fingers crossed that this one lives up to this skin-crawling trailer and the positive early reviews.