Knock once to wake her from her bed, twice to raise her from the dead..." So goes a disturbing urban legend involving an abandoned house supposedly inhabited by a vengeful, child-stealing witch. When troubled teen Chloe (Lucy Boynton) raps at the door one night, she has no idea the horror she's about to unleash. Fleeing to the country home of her estranged mother (Katee Sackhoff)-a recovering addict who's turned her life around to become a famous artist-Chloe must learn to trust the woman who gave her up years ago in order to stop the bloodthirsty, shape-shifting demon stalking them. This wild supernatural shocker delivers a barrage of nonstop jolts and searing nightmare images.