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(This review contains plot information regarding Harry Potter and the Cursed Child but only very mild spoilers.)

In 2013, J.K. Rowling wrote a short post (since deleted) on Pottermore, the official Harry Potter website, detailing her thoughts about using time travel as a device in literature. In the third book in the Harry Potter series, The Prisoner of Azkaban, Harry’s friend Hermione Granger uses a device called a Time-Turner to attend multiple classes in a single school hour, and the Time-Turner later factors into the plot when Harry and his friends use it to battle Dementors and help Sirius Black escape execution. “I went far too light-heartedly into the subject of time travel in Harry Potter and the Prisoner of Azkaban,” Rowling wrote. “While I do not regret it … it opened up a vast number of problems for me, because, after all, if wizards could go back and undo problems, where were my future plots?”

After Azkaban, Time-Turners were eradicated from Rowling’s magical universe. Hermione returned hers to Professor McGonagall, and all remaining instruments were apparently destroyed in a climactic battle in the Department of Mysteries in the fifth book, Harry Potter and the Order of the Phoenix, ruling out any more time travel. Rowling concluded the Harry Potter series with a natural leap forward, showing Harry and his wife, Ginny, saying goodbye to their second child, Albus Severus, on the platform at King’s Cross as they sent him off to his first term at Hogwarts. It seemed as definitive an ending as any, but it’s at that exact moment that the newest installment of Harry’s story picks up.

Harry Potter and the Cursed Child, the script of a two-part play that recently opened in London’s West End, is a faithful continuation of Rowling’s series that simultaneously breaks many of her rules. Although Rowling was involved in writing the story, the script is written by Jack Thorne, and the plot hinges on time travel in a way that prompts the question of how much Harry’s creator was involved, with wizards seeking to undo problems in a way that inevitably backfires. While almost all the major characters from the series return in some form or another, they’re less compelling than the two young heroes of the play, Albus Severus Potter and Scorpius Malfoy, the sons of Harry and his former rival Draco. As Albus and Scorpius struggle with living under the shadows cast by their fathers, Cursed Child too seems to wrestle with its legacy, borrowing heavily from older stories while simultaneously challenging the confines of their world.

Reading the next Harry Potter story in script form rather than in Rowling’s fluid, vivid prose was always going to be challenging for readers, so what’s most remarkable about Thorne’s work is how smoothly it flows. At its best, it’s as gripping as many of Rowling’s books were, with suspenseful plotting and twists that are just predictable enough to be gratifying. The stage directions are sometimes sparse, sometimes remarkably descriptive. (Here’s one after a Hogwarts student is drafted by the Sorting Hat: “There’s a silence. A perfect, profound, silence. One that sits low, twists a bit, and has damage within it.”)

The awkward hero of the first half is Albus Severus, Harry’s middle child, dwarfed by both his cocky, popular older brother, James, and his father’s impossible fame as The Boy Who Lived. The fourth scene of the first act, set in “a never-world of time change,” reveals glimpses of Albus’s increasing unhappiness after he arrives at Hogwarts, shows a disappointing lack of magical fluency, and is shut out by his fellow students. His one friend is Scorpius, a disarmingly sweet boy (in his first greeting with Albus, he literally sings about candy) who’s also an outcast because of outlandish rumors that he’s actually the son of … well, you know who.

It would be impossible to come up with a villain as cruel, malevolent, and outright fascinating as Lord Voldemort for the Cursed Child heroes to battle, so it’s almost poetic that Albus’s biggest enemy instead is his father. Thorne’s Harry Potter, all grown up, features prominently in the play, and the tension between him and his son is one of the most frustrating plot points, born out of dramatic necessity and riddled with cliché and angsty platitudes. “I didn’t choose, you know that?” Albus glowers in one scene. “I didn’t choose to be his son.” Later, Harry echoes the sentiment, saying, “Well, there are times I wish you weren’t ...” Although he immediately apologizes, why he feels this way is never really made clear; readers are left to intuit simply that the relationship is a troubled one.

Without revealing too much, Albus responds to his father’s outburst by conspiring with a mysterious young woman, Delphini, to go back in time and save one soul lost along the path of his father’s story. His motivation is shaky at best, but the decision pulls Albus, Scorpius, and Delphini into a montage of moments from Harry Potter history: The Tri-Wizard Tournament, a caper involving Polyjuice potion, the Forbidden Forest, a fearsome encounter with dementors. It’s familiar and well-worn territory at this point, and it might seem yawningly predictable if not for the shocking revelations that come in part two, many of which seem to destabilize Rowling’s universe rather than expand it.

Cursed Child, for one thing, seems fixated with chance, and the extraordinary power of twists of fate. The Harry Potter series always seemed to be a firm believer in free will—the power to change destiny by making specific and often difficult decisions. In the first book in the series, the Sorting Hat ponders whether Harry belongs in Gryffindor or Slytherin: “Difficult. Very difficult. Plenty of courage, I see. Not a bad mind, either. There’s talent, oh my goodness, yes—and a nice thirst to prove yourself, now that’s interesting … So where shall I put you?”

“Not Slytherin,” Harry thinks, gripping his chair. The hat goes along with his request. But Albus, by contrast, is given no such choice. And as his tweaks in the space-time continuum play out, futures are similarly reshaped and lines redrawn in the blink of an eye. Good characters go bad. Terrible characters reemerge. “It feels like we were all tested, and we all—failed,” says Scorpius.

The discombobulating influence of going back in time and making tiny changes is one Potter fans are well aware of by now. For years since the release of the final book, Harry Potter and the Deathly Hallows, Rowling has proffered hints and facts and tidbits that range from the remarkable (the beloved Hogwarts headmaster Albus Dumbledore was gay) to the banal (Teddy Lupin became a Hufflepuff). “The more Rowling enhances and embellishes her Harry Potter universe,” my colleague David Sims wrote last year, comparing Rowling to George Lucas, “the less room she leaves for readers to fill in the gaps with their own imaginations.”

Cursed Child, by this measure, is an act of overreach that feels mandated not by Rowling’s desire to fill out details but by an entertainment industry intent on reviving and rebooting anything that’s ever made money. Already, Warner Bros. (who produced all eight Harry Potter movies, which grossed more than $7.7 billion) has filed a film trademark for the title. The West End production is reportedly considering a move to Broadway. Harry Potter and the Cursed Child Parts I and II is expected to become the bestselling book of 2016: an extraordinary achievement for the published script of a play.

Reading Cursed Child, for all its compelling twists and turns, at many points feels like reading well-crafted fan fiction—the names are the same, and the characters feel familiar, but it’s apparent that they’re imitations nonetheless. It’s entirely possible that seeing the stage play, directed by the monumentally talented John Tiffany (Black Watch), is a different experience, and certainly there’s no sign of anything but a furious demand for tickets. But for readers, in agreeing to revisit characters whose stories have already been deftly wrapped up, Rowling risks undermining the powerful legacy she gave them in the first place.

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