Sally (Bailee Madison), a lonely, introverted child, has just arrived at the 19th century mansion her father (Guy Pearce) and his girlfriend (Katie Holmes) are restoring. While exploring the sprawling estate, Sally discovers a hidden , long-undisturbed basement. Unwittingly, she unleashes a race of malevolent, dark-dwelling creatures who intend to drag her and her family down into the mansion's bottomless depths.