What is Stranger Things: The First Shadow? This was not a question that bedeviled my 10-year-old son, happy as he was to be headed to Broadway and enfolded in the comfort of familiar IP. “I love Stranger Things,” William said.

But I was apprehensive. Stranger Things: The First Shadow, which opened at the Marquis Theatre in New York last week, after a successful run in London’s West End, is not a musical (thank God), but rather a play—not that you’ll spot that quaint word in many of the promotional materials. Nor does “play” adequately capture the ambitions of this production, which fairly earns one of those airy terms used by television marketers. A Broadway event? A Broadway…spectacular?

It’s a nearly three-hour act of fan service, filling in the origin story of Henry Creel, a misfit boy who becomes one of the Netflix series’s big, bad monsters (Vecna, in Season 3, per William). Henry will find his way to a sinister government lab by the end of the stage production, and, if you ask me, that’s where The First Shadow seems to have been born: It’s a play cross-bred with a roller-coaster, and maybe a haunted house.

I liked it. It is crisply directed (by Stephen Daldry), imaginatively staged, and well acted. I particularly liked the first hour, which was busy and headlong and had several unnerving, slightly assaultive sequences of sound and visual effects. By the end, I, a Stranger Things neophyte, felt sidelined by the lore, the world building, the inside jokes—but the shocks had had their effect: I was dizzy with ingeniously conjured spiders, snapped limbs, a disinterred dead cat, and a host of levitating actors. A giant ghoulishly tentacled puppet called…checks notes…The Mind Flayer had descended from the rafters to menace me. At the curtain call, I rose to my feet.

The Mind Flayer appears as a giant puppet descending from the rafters.

Photo: Matthew Murphy and Evan Zimmerman