Her willingness to put her characters in other hands is surprising, but Ms. Rowling said she had loved the entire process of cocreating “Cursed Child,” and hadn’t been prepared for the “emotional punch” the play delivered when she saw its final version.

She and her collaborators are also proud to have brought new audiences to the West End. Mr. Callender said that market research in the first year of the London production showed that 60 percent of ticket buyers were first-time theatergoers, and that 15 percent had subsequently bought tickets for other shows.

The Magic of Playacting

How to stage a Harry Potter tale without the benefit of the whiz-bang special effects movies can deploy? Mr. Tiffany approached the assignment with one guiding principle.

“The idea that the magic we put onstage could be a version of playacting stories in your bedroom,’’ he explained. “There was something about the aesthetic Jo had created, with cloaks and suitcases, that I wanted to harness directly and simply.”

Mr. Thorne predicted that even those loyal fans who’ve digested the best-selling script will be in for a surprise. “The stagecraft is such a massive part of the story that you still don’t know what will happen when you come into the theater,” he said.

Although the play will essentially remain the same on Broadway, the creative team is not taking anything for granted.

“If we see audiences aren’t getting anything, we’ll obviously adjust,” said Mr. Tiffany. “We’re always working on the show, and there are certain things about the architecture of the Lyric which means some things will change. It’s a theater with different kinds of possibilities, and I want to exploit them all.”