First of all, this film isn't NEARLY as bad as some reviewers on here would have you believe it is. Do unrealistic situations occur? Of course they do! It's called "suspension of disbelief," guys. You know, that mode your brain reverts to when watching the SAW movies of when viewing any James bond flick. You think, "Oh my god, that is so absurd; that could never happen!" but you let it go because you understand you are watching a work of fiction. In that regard this movie fits right in. Don't think so damn much about it and just enjoy the nonsensical ride.
Now, if after watching this, you want to see Luke Evans and Kelly Reilly in far superior thriller/horror films, check out their respective movies, No One Lives and Eden Lake. The latter contains one of my all-time favorite twist endings and is one of the most brutal films I have ever seen.