A reason behind my initial idea

I've been thinking about why a young girl would be kidnapping a young male, and why a film would start off with revealing that. One idea that I had to explain it was that the girl had kidnapped the guy who's father had murdered her parents when she was younger and she wanted revenge on their murderer so kidnapped his son. The film wouldn't actually have to be about her getting her revenge, it could focus on her parent's death and go back in time to show the story about how they died.
I'm not sure if I'm meant to be thinking about this kinda thing, but I thought I'd post it anyway =)