A woman trapped by a sadistic husband has to rely on unexplored strengths that emerge in a life threatening situation. This is not really a horror movie, although it's scary enough. Based on a Stephen King novel. I won't reveal how this plays out, but I felt it went off track at the end.
Carla Gugino is great, and deserves a lot of credit for making the script work. It's a very small cast of characters, but she really stands out in the way she manages the changes her character goes through. I think I'd like to read the book now.