He's stalked her for years. She's the one who got away. His first victim and the only one to escape. The one who's thought tortures him, arouses him. So, he stalks her. He's killed her boyfriends, unwilling to share her. He's slowly separated her from everyone, even her family. Finally, he's ready. She's alone, no family or friends. Her room is all set up for her training. He'll take her and teach her, turn her into his helper.
I want to play this through the initial escape, to the stalking and isolation and finally to the kidnap and training.