Playing over two nights in the Princess Theatre, Harry Potter and the Cursed Child drew gasps, laughs and pop concert levels of applause from an audience packed with devotees. And these days, who isn’t a fan of Harry Potter?

I’m reasonably familiar with it. I’ve read some of the books and seen all the films. But my friend Eva, sitting next to me during the two shows, is a proper diehard fan.

Growing up in Estonia, Eva read and re-read all the books religiously. When she was nine she transcribed a book of spells straight from Rowling’s texts and crafted her own wand from a crooked branch (concealing an actual peacock feather at its core).

Now she’s a filmmaker, and the Harry Potter films – as well as the audiobooks read by Stephen Fry – are a constant comfort to her. So I try to watch the play through her eyes. Eva doesn’t conceal her glee when the [SPOILER] turns up, or when [CENSORED] turned out to be [REDACTED].

(On the way out the door after Part One, audience members were handed badges asking us to #keepthesecrets, and I intend to, even though the script is available in every bookshop and the internet is full of spoilers. This is a safe space.)

I can reveal this much: told over six hours, Harry Potter and the Cursed Child picks up 19 years after the last book. Harry and his trusty pals Hermione and Ron are back, now played by an all-Australian cast – Gareth Reeves, Paula Arundell and Gyton Grantley respectively – but the focus is on their children.

Harry’s kid Albus, played by Sean Rees-Wemyss, is an average student living in the shadow of his rockstar dad. His best mate Scorpius, played with camp charm by William McKenna, couldn’t be further from his bully father Draco – and in my reading at least, he’s struggling with his sexuality.

The pair team up with Delphi (Madeline Jones), the 20-something cousin of long-deceased Cedric Diggory, and plot some misbegotten heroics of their own.

The production is ingenious, using just one adaptable core set which transforms throughout the show into everything from Platform 9¾ at King’s Cross Station to the Forbidden Forest. It’s controlled by what must be the hardest-working stagehands in Melbourne. The special effects are practical and clever without being showy, making the magic feel part of the world of the play. And even at six hours, the plot whips along at a frantic pace.

Plot-wise, the eighth story in the saga confirms a few things I always suspected about Harry and his world. First up, Harry is a bit of a dick. He rose from a Dickensian upbringing to become a revered hero, and yet here he is, 20 years later, a bureaucrat for the Department of Magical Law Enforcement. He’s putting undue pressure on his already struggling son Albus, who’s been sorted into Slytherin house, struggles with spells, and has a close friendship with the other school misfit, Scorpius Malfoy.

After the interval, Eva confesses it’s weird seeing Harry grown-up. “It’s disappointing,” she says. “I guess it’s inevitable. He went through all that and it was just to keep the status quo.”

Second, the world itself is an inherently conservative one. It harks back to a Britain that never really existed, one of gently drifting snow, charming terrace houses and school spirit. Harry is raring to send his son off to boarding school, saying it will “make him”, but doesn’t want him hanging around with the Malfoy boy because of a decades-old beef with his father Draco (Tom Wren). Harry’s married to his best mate’s sister, and he uses his government position to lean on teaching staff at Hogwarts. What a boring and mediocre man Harry Potter has become.

It’s a relief, then, that the new kids are a bunch of misfits, and the play is most fun when they’re onstage. They’re not heroes, they’re relatives of heroes, struggling with not being normal instead of being exceptional. Well, relatively normal, given they’re all students at a magic school.

The stakes are high, and not just in the Harry Potter world. The Cursed Child adds new avenues to a vast and detailed chronicle, and the fans take it very seriously. After one revelation about a much-loved character, a child behind me turned to her father and whispered, “Is that true?” Sorry kid, it is now.

The play is steeped in continuity, but it’s also a bit like fan fiction, with references to previous characters, plot points and devices. The background research is about 4000 pages of reading, or 20 hours of movie-watching. Barely a scene goes by without references to the past – some fleeting, many vital to the plot. It stretched my memory a few times and stretched my credulity a few times more. Though there are new characters, there are very few new big ideas, so at times I missed the inventive flourishes of the books.

Normally I’d say that’s a risky approach – potentially alienating a general audience with convoluted backstory – but like Star Wars before it, Cursed Child uses its longevity, and the audience’s detailed knowledge of its past, to address intergenerational trauma. Every action is motivated by prior actions stretching back a generation or two. Harry’s continuing dickishness, the way he bestows his hang-ups and prejudices onto the next generation, is explainable – even realistic. And while I wish it added something new to the mythology, Cursed Child wears its baggage with pride.

On the way out the door, excited audience members are meeting the cast – or the muggles pretending to be wizards (sorry Eva). I pass the merchandise counter, heaving with people buying scarves, wands and books. I ask the attendant if many people buy Slytherin merch. “Sure,” he says. “Second to Gryffindor, probably.”

It’s reassuring to know that the Hogwarts students sorted into the evil house (a cruel tradition, even for a boarding school) have been given a shot at being the heroes – both in the play and in the imaginations of kids getting around wearing Slytherin scarves.

Eva asks me if I know what house I’m in. Ravenclaw, I tell her. We did a quiz in the office. She looks me up and down and nods wisely. “That makes sense,” she says.

I have no idea what she means, but as with the last six hours, it’s nice to have a sense of belonging and a connection with a past, even if it’s not mine.

Harry Potter and the Cursed Child Parts One and Two is playing now at the Princess Theatre, Melbourne.

harrypottertheplay.com/au