When Susan sees the girl in the photo on her wall blink, she blames exhaustion. But the shadowy figure that follows, and the escalating episodes of terror that ensue, are harder to dismiss. The police find no evidence of an intruder, and with each frantic call, their skepticism grows. Friends and family grow concerned, but no one sees what Susan sees. As her mental state deteriorates and the line between reality and delusion blurs, Susan loses all credibility, until the night she's found bloodied and broken in her flat.

Everyone assumes Susan is losing her mind. But something is watching. And it only moves when she blinks.