Horror movies work best when they have a resonant subtext. Like good science fiction is always about the present, good horror movies are about human experience. When they set up a metaphor, though, they have to follow through. This one didn't, which is a real shame. It had some good performances and great scares. But the story it was trying to tell about unresolved trauma is undone when it doesn't follow its own rules and relies on hackneyed tropes instead.