(CNN) -- He's terrified millions of children with his books, from "Welcome to the Dead House" to "Planet of the Lawn Gnomes." But R.L. Stine isn't ready to let his audience grow up in peace.
With the 20th anniversary of his popular "Goosebumps" series comes Stine's adult horror novel "Red Rain." The book follows travel writer Lea Sutter into the middle of a devastating hurricane and out again with a pair of evil twins who will wreak their own kind of devastation on her family.
Stine isn't the first young-adult author to venture into adult fiction. J.K. Rowling recently released a novel titled "The Casual Vacancy" that sold 157,000 hardcover copies in its first week of publication, according to Nielsen BookScan. Beloved "Sweet Valley" creator Francine Pascal has also moved into the adult world with her characters; Elizabeth and Jessica Wakefield grew up in "Sweet Valley Confidential" and started their 30s in this summer's novella e-series "The Sweet Life."
"Red Rain" isn't even the first adult book Stine has written. In 2000, he released a novel called "Superstitious" about a professor named Liam O'Connor who is the most superstitious man in the world, for good reason. Stine's publishers expected a best-seller, but book sales were mediocre for an author with such a big reputation.
"It was too early to do an adult novel. No one asked about it. ... I've been waiting by the phone for 12 years," Stine joked.
This time, his fans are ready. They've been hounding Stine on Twitter -- he has almost 60,000 followers -- asking him to write a book for them.
"That's how I keep in touch," Stine said. "There are no kids on Twitter. It's all people (in their 20s, 30s) who read 'Goosebumps' and 'Fear Street' in the '90s. They were my huge audience."
Stine has written more than 300 books that have sold a combined 350 million copies around the world. (At one point, he was churning out 12 "Goosebumps" books a year; now he's down to six.)
At the recent National Book Festival in Washington, the author's autograph line seemed endless.
"It was amazing. It was 7-year-olds, 10-year-olds, 20-year-olds, 30-year-olds. Half of them were like, 'I loved your books when I was a kid,' " Stine said. "It's great for my ego."
Stacy Creamer, editor for "Red Rain" as well as the vice president and publisher for Touchstone, knows Stine's work well. Her 10-year-old son devours his books "like crack."
"To see that kind of enthusiasm in my own son, it was easy to see if, you know, someone checked in with him 10, 15 years from now. ... I think he'd be pretty intrigued."
Stine sent Creamer an outline for "Red Rain." The plot he wanted to tackle seemed so complicated, Creamer was a little nervous. But after receiving the finished novel, she said, she would have published the book even from an unknown author. Of course, having Stine's name attached added a bit of glamour.
"I knew he had the chops to do it, because I think writers are writers," Creamer said. "But man, he just slammed it."
There are pitfalls to having a children's author write an adult novel. Although Rowling's "The Casual Vacancy" is on track to become one of the best-selling hardcover novels of the year, it has received mixed reviews.
"After all of this magic, what could we have expected?" professor Seth Lerer wrote for The Daily Beast. " 'The Casual Vacancy' may be a disappointment, but it is a natural one. For after having written books of magic for a magical age, Rowling has come out with a book of Muggle life for Muggles. Is this what happens when you grow up?"
Pascal's "Sweet Valley Confidential" ended up on best-seller lists as well, but fans were outraged at the experiences Pascal crafted for her once-innocent teen characters.
"I felt a 27-year-old woman (Elizabeth) was entitled to an orgasm," Pascal said with a laugh. "You would be surprised at how many responses I got that didn't feel that way. ... I had somehow maligned their hero, and it was not good."
Pascal's idea for an adult novel came in a similar way to Stine's. Facebook was her inspiration; on the social media site, she said, everyone is looking for the kid they grew up with, the friend from elementary school, their high school sweetheart.
"Strangely enough, even though these are fictional characters, they are real (to fans)," Pascal said. "I thought they would have a curiosity to find out what happened to these people they lived with."
Curiosity seems to have outweighed outrage for the millions of Sweet Valley readers. "The Sweet Life" e-series was downloaded more than 40,000 times. A copy of all six novellas will be available in one hardcover book October 30.
Stine won't have to wait long to see whether "Red Rain" is a success; the book is released Tuesday. If it is, he just might continue to give his grown-up fans goosebumps.
"I'll wait by the phone, see if it's another 12 years," Stine laughed. "I'd love to do another one."
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