Social worker Emily Jenkins encounters a mysterious file known as Case 39. She rescues a ten-year-old girl named Lilith from her abusive parents and decides to take the child into her home temporarily. However, mysterious and terrifying events soon begin to occur around the girl. Emily's colleagues and friends die under strange circumstances, leading her to realize that an ancient and dangerous evil is hidden behind the child's innocent appearance. Now, she must fight for her life and attempt to stop this mystical horror.