When a rehabilitated pyromaniac finds acceptance in a group of satanists with a manipulative but charismatic leader, she must prove her worth by burning down the Notre Dame.

“burn a church” because it’s a [pyromaniac + satanists] plot. Make the church as big and important as possible. Raise the stakes.

“prove her worth” to the cult’s leader, a mother/father figure. This will create an inner conflict and a journey. She thinks she must prove her worth to her new family, by doing as they say, but she knows it’s wrong.

“rehabilitated” because it implies backstory, addiction, relapse, weakness, but also an effort to get better.

“find acceptance in a new family” because it implies rejection from her own family. I always find it interesting as a backstory. In Boogie Nights, Dirk Diggler gets rejected by his mum, but he finds a new family in the porn industry.

“manipulative” or “obsessive” because it implied that the leader considers their cause more important than the relationship with the protagonist?they will use her.

The leader can be male or female, depending on the dynamics you want to give. She will be a mother figure or he will be a father figure?this will blend with the protagonist’s backstory wound.

I don’t know if this is the story you want to tell, but I am totally hooked.