Naomi Ragen writes fiction to inform and effect change, not necessarily to entertain, which is important to know before you pick up her first true-crime novel, “The Devil in Jerusalem.”

It is sharply written, educational, hard to put down and well worth reading, but the tale of a Haredi family in Jerusalem succumbing to horrifying abuse is not an easy or pleasant experience.

“This book took so much out of me,” Ragen said. “It was a horror to go through that court testimony and read what those kids went through. It was a very difficult book to write.”

Naomi Ragen says it has taken a lot of time to recover emotionally from writing this book.

Naomi Ragen says it has taken a lot of time to recover emotionally from writing this book.

The court testimony related to the case of Elior Chen, a self-proclaimed Jerusalem rabbi who was convicted in 2010 of horrific abuse of eight children through the manipulation of his disciples, including the children’s mother.

The case connected with questions that Ragen said had been on her mind for years. “What has happened to the Jewish religion the past 40 to 50 years since I was going to day school in Far Rockaway? All anybody talks about is Kabbalah and wonder-working rabbis and praying to graves and angels. What has happened to this rational, beautiful religion that I was taught and grew up with?”

She approaches that real-life mystery through her novel’s investigation into what happened to two boys brought to a hospital hours apart after suffering life-threatening abuse.

At the heart of the fictional mystery is the behavior of the young mother, who shows no emotion about her suffering sons and breaks her silence only to tell obvious lies to the police and to ensure that her other children say nothing.

Ragen said a challenge for her as the writer and for readers is to get past hating the mother for failing to protect her children. She said she and her police protagonist, Detective Bina Tzedek, had to go through the same process to understand that the mother also was a victim and that she was neutralized by classic cult mind-control techniques.

It’s also important to understand that although the abuse in “Devil” occurs within the setting of Jerusalem’s Haredi community, the culprits are part of a cult, not ultra-Orthodoxy. The techniques and the violence could occur in any cult.

“Any time you stop using your brain, it’s not a religion; it’s a cult. If you can’t question things, that’s not Judaism, and you should run in the opposite direction as fast as you can,” Ragen said. “If this book doesn’t do anything else, I hope it does that.”

One of the ironies she learned in researching the novel is that cults, which demand that people not use their brains, find the most fertile recruiting ground in institutions such as Harvard and Yale. Cults prey on people who are intelligent enough to search for something beyond the ordinary.

Ragen hopes that her storytelling helps save people from falling victim to cults.

“A novel can only touch people’s hearts and try to inform them,” Ragen said. “I’m not a social worker or psychologist. I wrote a work of fiction. I do hope that their minds will be alerted to the predators that are lurking around, the predators of holiness. When you send your kids to Israel for year programs, be forewarned. These kinds of predators are out there.”

The Devil in Jerusalem

By Naomi Ragen

St. Martin’s Press, 320 pages, $25.99

At the festival Nov. 9