One of the most traumatic periods in Jonathan Stroud’s childhood had a positive aftermath. The author of the Bartimaeus fantasies, who is launching another middle-grade series this fall with Lockwood & Co.: The Screaming Staircase (Disney-Hyperion, Sept.), was very ill, he recalls, between the ages of seven and 10. He read “furiously” during the days when he remained home from school or even had to go to the hospital for extended stays.

“I was in need of something that would give me an escape, and stories with magic and the supernatural provided that,” he says. Stroud now pays it forward by striving to provide for his readers that same degree of escape into fantastical worlds that he so craved as a boy. He constantly tries, he adds, to write a book that gives him “pleasure as a jaded adult novelist as much as it gives pleasure to a 10-year-old. When I write something that would have made me laugh as a 10-year-old, or would have scared me or would have excited me, I know I’m onto something.” His publisher thinks so, too: The Screaming Staircase is being released with a 100,000-copy initial print run.

While the Bartimaeus series was what the author calls “an out-and-out fantasy with lots of magic,” he says that the Lockwood & Co. series will be a little darker and a lot more thrilling: there’s an epidemic of supernatural appearances throughout London, and only young people have the psychic abilities required to confront and eradicate the ghosts and other malevolent spirits popping up all over the city. Consequently, psychic detective agencies staffed by preteens are also popping up, including Lockwood & Co., a small firm run independently of any adult supervision.

While Stroud’s nine-year-old daughter, Isabel, just this year read the Bartimaeus series, he’s hesitant about letting her read The Screaming Staircase, or the second book in the series, The Whispering Skull, which he’s currently writing. Even though Isabel has provided him with ideas, insights, and lists of different ghosts he should include in the series, Stroud thinks she should wait another year. “It’s too scary,” he says. “I don’t want her running for the hills.”

The author signs advance copies of The Screaming Staircase during a ticketed autographing session today, 11:30 a.m.–12:30 p.m., at Table 7.