Fourth Closet by Scott Cawthon

John and his friends race to stop a returning killer and his murderous animatronics as children begin disappearing again, unraveling the shocking truth about Charlie’s identity and her father’s desperate creations, including a hidden chamber tied to an old tragedy. Their investigation leads to a robotics facility and remnant-fueled experiments, culminating in a perilous rescue and a final showdown to free tormented spirits, with heartbreaking sacrifices along the way.