I don't know what to make of this movie. Total spoilers
Consider this from a first viewing, not after knowing about the "twist".
So, you sit down to watch, and at first the movie has this great vibe going for it. It was tense, and creepy.
Then (still not knowing about the "twist"), instead of doing what any normal person (or even a typical slasher movie victim) would do (hide in one spot, and sit still, or run screaming), she starts poking around like she's looking for something, and we have no idea what it might be, but it certainly doesn't seem to be her father, the stalker, a place to hide, or a way out.
It wasn't as effective as it might have been. I couldn't stop wondering why she was looking on bookshelves, in corners, in cupboards. It made no sense at all at that point in the movie, and made it very hard to maintain my suspension of disbelief. I didn't see anything indicating she was looking for keys, till she found one 30 mins later. Were we supposed to assume that was what she was doing?
Then you have the scene of someone looking for her in the one solitary moment she does hide, and the flashes of creepy little girls, and someone coming at her with a knife. Does it set things up for the "twist"? Sure, but to make you assume that she was hallucinating in retrospect is a bit much. Leading you to assume she was hallucinating the whole time seemed like a tacked on excuse, rather than an actual part of the story.
And what's with the story in the first place? Who the hell was the other guy? Did they live in that house, and she was his wife? Was she their sex slave? Was there father-daughter molestation occuring? Was that even really her father? Did he/they make her abort her pregnancy? Did they kill the child?
And in particular relating to all of the above, wtf were they thinking taking her back to that house if any of the sordid stuff that is hinted at actually took place? Did they think she wouldn't remember? Not to mention, while laura may have been the same girl from the photos, to be quite frank she didn't look like her to me. Especially in light of the one guy saying no one had lived there for years. Laura looked like she was late teens early twenties to me, certainly not old enough to have lived in that house, been gone for years and come back to it.
And who made the noises at the beginning that her father went to investigate? Are we supposed to assume the entire movie was a hallucination? If you want to go down that road, perhaps the house was a hallucination, maybe she never killed anyone, maybe the whole movie actually took place inside her head at an insane asylum.
Based on a true story? A story where some guys had a sex slave they kept in a house long enough to get her pregnant, and get rid of the child, then took her back to the house to fix it up to sell? If she was that nuts, surely there were indications of it before they went back to the house. And as someone else said, if this was all one shoot, precisely when was she supposed to do her killing? There isn't a moment we don't see her. And if it was all hallucinations, then it wasn't real time, regardless of how they filmed it.
This movie makes no sense at all, even if you are being lenient and assume she was hallucinating. Personally, I think the "twist" was that the writer's didn't know where to take the story, and tacked it on like a "deus ex machina". Or the "true" story is simply that they went back to the house, she went nuts, killed them both, and disappeared, no creepy omg who is after me, who is in the house with me stuff. If it is a true story, how would they know that anyway, since the guys were both dead, and she disappeared.
Don't get me wrong, it had a fantastic atmosphere, it's worth watching for that alone, but the plot makes no sense, and it expected you to assume way too much.