In King's Cross railway station, at the approximate location of Platform 9-3/4, there bustles a small commercial temple of the multibillion-dollar Harry Potter kingdom. Within the well-stocked walls of the Harry Potter Shop, you can conduct a merchandise sweep the likes of which might cause even He-Who-Must-Not-Be-Named to collapse in swooning contemplation of licensing checks yet to be cashed.

Wizard chess sets, Gryffindor hoodies, book bags in Slytherin green and Hufflepuff yellow, scarves, wands, Dobby dolls and Hedwig keychains. For 9.50 pounds (about $13), you can have your photo taken with the added caption, "Have You Seen This Wizard?" For 15 pounds ($21), they'll create a personalized acceptance letter to Hogwarts for you. At 11 a.m. on a recent Friday, the line for a chance to pose under the Platform 9-3/4 sign — the magical spot where Hogwarts-bound students pass through solid brick to board the school train — was 40 tourists deep.

It's breathtaking, really, the array of items and the scale of the mercantile imagination — including, of course, the Harry Potter theme parks, the Lego sets, the video games — unleashed by J.K. Rowling's seven Potter books and eight motion pictures. Estimates of the value of the enterprise range up to an astonishing $25 billion.

And now, yet another Potter bauble is being peddled, one that is a lot more expensive than those that fill the shelves at King's Cross. This would be the stage production that began running last week at the massively overhauled Lyric Theatre in Times Square in New York: "Harry Potter and the Cursed Child," a two-part, 5-1/2-hour stage sequel to the mega-popular Potter franchise.

The double bill has been playing to sold-out houses in London's West End for nearly two years, and now the Broadway incarnation, which features seven actors from the London original — including those who portray grown-up Harry Potter (Jamie Parker) and Hermione Granger (Noma Dumezweni) — is pretty much guaranteed to be a long-term tenant for the Lyric. As of early March, premium tickets (on sale already through March 10, 2019) could be found on the Ticketmaster website. Two seats in Row D in the orchestra for each of the play's two parts in late March could be yours for a total of $1,217.50, including $58 in service fees; on the scalping (or resale) websites, tickets are being hawked for between $300 and $1,000 apiece.

This is all good for the theater, is it not? A pair of shows with a certified fan base, a smash hit before its final dress rehearsal, a fantastic draw for families with a desire for comfort-food entertainment?

Well, maybe.

"Harry Potter and the Cursed Child" is a boon to Broadway in the sense that it bolsters a burgeoning entertainment business model, one that more than anything appreciates a sure thing. The production solves a real estate problem: what to do with a barn of a theater first refurbished in 1998 as the Ford Center for the Performing Arts (and later, the Foxwoods) that has proved difficult to fill successfully. And it nourishes a market that is ever more dependent on tourists, who now buy two out of every three Broadway tickets.

Still, despite the prizes the production has won and the critical plaudits it has received, the plays that have been concocted for the stage by Rowling; the show's director, John Tiffany; and playwright Jack Thorne are more commerce than art.

"Harry Potter and the Cursed Child" is less a dramatic investigation than a live dive into the fantasy genre. It's two evenings of what you might term spectacular fan fiction. I saw the plays in London late in 2016, and although the designers display heroic levels of invention — people such as Jamie Harrison, who is credited with the illusions and magic, and set and lighting designers Christine Jones and Neil Austin — this stage addition to the Potter canon has been developed with the die-hard devotee in mind.

Will many people who are not already steeped in Potter lore be held for nearly six hours of a heavily nostalgic brand of exposition? In London's Palace Theatre, I watched my wife, who barely paid attention to my daughter and me over the years when we ruminated over the death of Sirius Black or tested each other's knowledge of patronus charms, struggle to engage with a parade of familiar characters (and a few new ones) during the two-part drama.

Granted, in making Hogwarts kids fly on brooms, or simulating the turning back of clocks through a device Rowling and company call the Time Turner, the plays accomplish the delightful feat of revealing the clever ways the stage can compete with cinematic effects. Or rather, not so much vie as develop its own magical language.

Harry and Hermione and Ron will find a welcome home on the new Broadway, and the plays in the Lyric will keep the Potter machine minting money. As to whether these franchise extensions as theater are a healthy development for the world of the stage, count me among the unconvinced.

If you go

What: "Harry Potter and the Cursed Child"

Where: Lyric Theatre, 214 W. 43rd St., New York

When: Previews begin tonight, March 16, and the show officially opens April 22

Tickets: $20-$289

Visit: harrypotter.ticketmaster.com