This movie is the first half of what could be something interesting, unfortunately this ends without explaining what's happening.
There is some interesting setup and some interesting questions are raised but the movie fails to deliver on any of it.
The events in the movie indicates this isn't the first time someone has mysteriously vanished from this town. That's cool but if you're looking to understand why there is no answer. There is subtext to read into indicting that anyone else has any idea either.
There is a lot of drama and some excellent tension but the viewer is left with nothing when the movie suddenly ends the credits roll.