Part of Raising Cain's plot is when Jenny finds Nix Sr. holding Amy hostage as part of his control group to study the development of MPD.
Dr. Carter Nix is a respected child psychologist. His wife, Jenny, becomes concerned that Carter is obsessively studying their daughter, Amy; he regards her like a scientist tracking the development of his creation. But Carter himself suffers from multiple personality disorder; his alternate personalities include Cain, a violent petty criminal, Josh, a shy 7-year-old boy, and Margo, a middle-aged nanny who protects the others at all costs. Jenny follows a woman who she thinks is Waldheim to a motel, but it is actually Carter/Cain. She follows Carter/Cain, who is now Margo, into an elevator. When it opens, she sees Nix Sr. holding Amy hostage. He had been using Carter and his multiples to procure the children so he would have an adequate control group to study the development of MPD. 
