LONDON (AP) — There are fans with wands and wizard costumes, midnight book parties and throngs of excited muggles. Harry Potter’s magic is back.

Nine years after J.K. Rowling’s final novel about the boy wizard, Harry has returned, on the stage and the page — and he’s still producing commercial alchemy.

“Harry Potter and the Cursed Child ,” a two-part stage drama that picks up 19 years after the novels ended, has its gala opening Saturday at London’s Palace Theatre. It’s already a hit. Although producers won’t release ticket sales figures, the show is largely sold out through December 2017; another 250,000 tickets will go on sale Aug. 4.

“It is event theater in the truest sense,” said theater commentator Terri Paddock, who co-founded stage website MyTheatreMates. “You can’t turn up at the Palace Theatre and not get caught up in the excitement. There is such a buzz: passers-by stopping and staring … children with their capes and wands and wizard excitement.”

It is not just the theater that is seeing a Potter-related boom. Booksellers expect a bonanza when the script is published Sunday. Thousands of bookstores around the world are holding midnight Potter parties Saturday, and are reporting advance sales not seen since the 2007 publication of “Harry Potter and the Deathly Hallows,” the final novel in Rowling’s seven-book series. North American publisher Scholastic has printed 4.5 million copies, according to Publishers Weekly.

“Cursed Child” is not a novel, and it’s not primarily written by Rowling. She helped develop the story, but the script is by playwright Jack Thorne, whose work includes the stage adaptation of a Swedish vampire story, “Let the Right One In.”

But that doesn’t matter to Harry’s many fans.

“There is huge excitement,” said Melissa Anelli, webmistress of Harry Potter website The Leaky Cauldron. “It’s the next piece of the Harry Potter canon that we love.”

Britain’s Waterstones bookstore chain is holding book launch parties at 140 stores, including a bash over four floors of its London flagship store complete with themed refreshments, quizzes, props from the movies and a quidditch team.

“I don’t think it gets bigger or more exciting than Harry Potter, both for readers and for our booksellers,” said Sandra Taylor, head of events at Waterstones. “There are so many booksellers I talk to who became booksellers through falling in love with Harry Potter,”

Rowling has long insisted there will be no new Harry Potter novels, so excitement about the new stage story is stratospherically high. She created the story for the drama alongside Thorne and director John Tiffany, who helmed the Tony Award-winning musical “Once.”

It runs for five hours over two parts, which can be seen on separate evenings or during two-show days.

Last seen as a teenage wizard, Harry is now an overworked civil servant at the Ministry of Magic, while his son Albus is a pupil at Hogwarts School of Witchcraft and Wizardry. The producers’ synopsis says that “while Harry grapples with a past that refuses to stay where it belongs, his youngest son Albus must struggle with the weight of a family legacy he never wanted.”

Beyond that, few plot details have leaked during almost two months of previews. Audience members are given buttons urging them to #keepthesecret, and most have complied.

Critics have also avoided spoilers, stressing spectacle instead of plot in their reviews. Variety dubbed the show “spellbinding” and “total theater,” while London’s Daily Telegraph said it would “raise the benchmark for family entertainment for years to come.”

Since finishing the Potter books, Rowling has written a novel for adults, “The Casual Vacancy,” and three crime thrillers under the name Robert Galbraith. She has also kept a foot in Harry Potter’s world with the screenplay for “Fantastic Beasts and Where to Find Them,” a film set in the same magical universe as the earlier stories.

“Cursed Child” would seem ripe for a movie adaptation, but Rowling’s spokeswoman says there are “no plans for there to be a film.”

The play is drawing a markedly younger-than-usual theater crowd, and London’s theater world hopes it may bring a new generation to theatergoing, much as the novels inspired countless kids to love reading.

Paddock said her fears that the show might feel exploitative — a finely crafted cash cow — were unfounded.

“It feels really celebratory and welcoming,” she said. “I think it will be in the West End for a long time.”

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Follow Jill Lawless on Twitter at http://Twitter.com/JillLawless