“Why is everybody staring at us?” asks young Albus Potter nervously.

Better get used to it, kid.

Harry Potter and the Cursed Child has pulled off a transfiguration challenge worthy of Professor McGonagall: Converting the visually arresting world of Harry Potter into stage play. Currently in previews and officially opening July 30 in London’s West End, Cursed Child goes far beyond dutiful brand extension with an entirely original and hugely ambitious sequel to the Potter books, presented in two parts and nearly five hours long. Author J.K. Rowling, working with London theatre veterans Jack Thorne and John Tiffany, have delivered a production that’s as spectacular as it is ambitious, stuffed with special effects and twists that had a preview audience gasping, Cursed Child is a story that doesn’t play it safe with the Potter canon and will change how fans see certain favorite characters forever.

The plot, kept under an invisibility cloak of secrecy until now, has a very grabby premise. (Spoiler alert: The following three paragraphs will discuss what happens during the first half of Part One. Given the mounting excitement in the theater as fans realized where the story was heading, revealing this feels a bit like opening somebody else’s birthday present, so skip this portion to remain in the dark).

Cursed Child starts precisely where the books left off, staging the epilogue from Deathly Hallows where a 40-year-old Harry (Jamie Parker) and his wife Ginny (Poppy Miller) gather at King’s Cross Station to send their middle child Albus Severus (Sam Clemmett) off to his first year at Hogwarts School of Witchcraft and Wizardry. Albus frets that he might get sorted into the dreaded Slytherin House. Following an instantaneous change from muggle clothes to Hogwarts uniforms, Albus’ fears are realized when The Sorting Hat places him into the house associated with his father’s enemies. Equally scandalous, Albus befriends Scorpius Malfoy (Anthony Boyle), son of Harry’s childhood nemesis Draco (Alex Price), who bears his father’s pale hair and skinny frame, but seemingly none of his cruelty. Albus and Scorpius are both struggling under the crushing weight of their family’s opposing reputations and even their own names — Albus Potter is neither as wise as the famed Headmaster Dumbledore, nor as capable as his father (when it comes to riding a broom, Albus literally can’t get it up), while Scorpius doesn’t want to sting anybody (so naturally he’s tormented when he hears rumors that he’s secretly the son of Lord Voldemort). The story’s action mainly takes place during the duo’s fourth year, when an outlawed Time-Turner is discovered that grants the power to travel many years into the past. An increasingly bitter Albus, resentful of his father’s insurmountable legacy, hatches an audacious and dangerous plan to correct one of his father’s biggest “mistakes.'”

The time-travel storyline lets Cursed Child have it both ways, with a forward-spinning tale that also revisits iconic moments from the saga’s past — it’s like the Back to the Future II of the Potter-verse (It’s your kids, Harry! Something’s gotta be done about your kids!), with Rowling remixing popular elements from her middle stretch of Potter books. Cursed Child has the time-travel of Prisoner of Azkaban, tackles key events from Goblet of Fire (Rowling’s finest and most perfectly structured novel), resurrects the teen anger of The Order of the Phoenix, and has a titular mystery like Half-Blood Prince — who is the Cursed Child?

You’ll notice I’ve barely mentioned the title character; it’s Hogwarts: The Next Generation that drive the action in this story. Yet the original heroic trio of Harry, Hermione (Noma Dumezweni), and Ron (Paul Thornley), have plenty to do too. Harry is a Ministry of Magic worker whose scar is hurting again for the first time in 19 years while he ineffectually uses his wand to shuffle papers on his desk. Hermione has ascended to Minister for Magic and worries that creatures who once supported You Know Who might be gathering for some new dark purpose. Her husband Ron happily runs Weasleys’ Wizard Wheezes, and per usual has some of the best lines (telling Harry, “Your scar could be hurting because you’re getting old”).

The playwrights have stated the reason for the two-part format is the “epic nature” of the story, and that’s not an exaggerated description. There’s enough plot in Cursed Child (with 42 actors playing a variety of characters) to frame an 800-page eighth Potter novel. The play’s rehearsal script will be published July 31, and it’s breaking pre-sale records, but one wishes the tale existed in novel form; the Potter-verse feels somehow incomplete for such a version not to exist. Hardcore fans will definitely be pleased; the preview audience gave the final curtain a rapturous response, with one theatergoer declaring during an intermission, “I need to see it again.” (Good luck with that — the show is sold out through next May, though 40 tickets are being released online each Friday, and look rather like Wonka’s golden tickets).

But seeing the play later rather than sooner is probably not the worst idea either: All the components are there for greatness, but this not-final preview version I saw last week was a potion that the perfectionistic Severus Snape would brew longer before serving up. Thankfully, it’s far more difficult to deliver what the play does well than to improve upon its stutters. Part One in particular seems a bit overstuffed — with some lengthy exchanges and a couple unnecessary scenes that could be cut altogether. The production needs more moments to let the actors take a breath and play their roles rather than speeding through pages of script faster than Harry on his Firebolt. “You talk too much,” one character declares, but the same could be said for nearly everybody.

Yet there’s something comfortably familiar about the excess too. It’s been nearly a decade since we’ve had a new Potter book and the film adaptations were largely tightly produced studio products. Some of the tendencies that critics might describe as flaws (such as abundance of exposition) also remind you of the joy of reading the Potter novels. In that respect, Cursed Child feels more like loyal adaption of Rowling’s writing than the films. If the movie-version of The Prisoner of Azkaban was 5 hours long and Rowling had final cut, the scenes would flow more like this. Still, it’s a problem when the audience is largely applauding Part One’s special effects (Part Two, which leviosas the story’s stakes through the roof of the Palace Theatre, is far tighter).

Speaking of the effects, this is Harry Potter, so you expect to see magic, and you’ll get plenty. There’s slight-of-hand, trap doors, wire flight, quick change, and smoke and mirrors galore. The cast seemingly had to become nimble amateur magicians to pull this off, and it’s impressive how many spell-casting elements of the Potter universe director Tiffany managed to portray in a live act (just don’t expect to see, like, Quidditch). During the preview I saw, each effect was executed almost flawlessly (though the Potter franchise should probably just avoid trying to pull off centaurs all together). At times the production seems like a complex miracle of blocking and stage direction, and with all the fire being thrown around you worry for the actors’ safety (one repeated gag has characters arriving through a lit fireplace — via floo powder, don’t you know — the flames going out and springing back as they slide out onto the stage).

The performances are naturally the most work-in-progress aspect. There are shouted deliveries that recall Rowlings’ Order of Phoenix-era tendency to floor her caps-lock to prove characters are REALLY UPSET. As a grown-up Harry, laden with responsibilities that he’s unsure how to handle, Parker certainly looks the part and seems to have taken a couple cues from Rowling’s characterization and also Daniel Radcliffe’s performance in the films. Dumezweni’s Hermione heartily captures her character’s sternness but the script has unfortunately shed the fan favorite’s infectious passion and curiosity (blame the passage of time?). Best of the trio is Thornley, whose dad-joke-ready Ron seems spot-on. The three are like a distant radio signal of character familiarity, drifting in an out, intermittantly channelling their iconic past.

Among the younger actors, Clemmett’s Albus is strong, though could benefit from some sympathetic tuning amid his waves of teen bitterness. The play’s most unexpected edition is Scopious, played all slumped and uncertain by Boyle; he’s an entirely new character who’s fully realized and compelling. Together they’re the heart of this new tale, which ultimately seeks to wrestle with the heady challenges of parenting and the less-certain responsibilities of being a parent’s child. As Draco surprises us by saying at one point: “People say parenting is the hardest job. It’s not. Growing up is.” It’s those developing years that leaves everyone feeling like they’re on stage, in the spotlight, and cursed.