LONDON, June 8  — When we last left Harry Potter, in the final pages of J.K. Rowling’s Harry Potter and the Deathly Hallows, he was a middle-aged wizarding bureaucrat sending his second child, Albus Severus, off to Hogwarts for the first time. 

After the violence and darkness that had marked Harry’s younger years in Rowling’s story, life seemed to have turned out happily for him and his friends.

Now Harry is back — in a play, this time — and all is not well. 

Harry Potter and the Cursed Child, which had its first preview in London today, immediately thrusts the audience back into the concluding scene from Deathly Hallows, rushes rapidly forward a few years, and then shoots off into all sorts of unexpected directions. 

The action is as dense, complicated and plot-heavy as we’ve come to expect from Rowling, and the play concerns itself with (among other things) the acute growing pains suffered by a highly unhappy Albus as he tries to make peace with his family, his friends and himself.

The play seems like a Valentine’s card to people who love the Harry Potter books. 

Here are all the characters we’ve come to know over the years: Harry, now married to Ginny Weasley; Hermione and Ron, now married to each other and behaving, at least at first, in their old familiar ways. 

Here are a host of other characters, many of them making what amount to quick cameo appearances. Here is a second generation of new characters, including Scorpius, the unexpectedly delightful son of the decidedly undelightful Draco Malfoy, and of course the troubled Albus, the focus of the plot.

(NOTE: Fans not going to the show who don’t want to find out what happens until July 31, when the text of the play is to be published, might want to disapparate out of their seats for the next two paragraphs. In any case, we will try to keep it vague.)

Exciting scenes feature, among others, the Sorting Hat (wittily staged); the grumpiest of the centaurs, who is extra grumpy this time around; and one of the book’s more diabolically unpleasant characters, who turns up at the end and who we had hoped we saw the last of. 

The tantalising question arises of what might or might not happen to the present if you try to tamper with the past. 

Albus Dumbledore himself appears, in a painting that speaks to us, as paintings do in Potter-world, followed by as good an explanation as you’ll ever hear of why we should not mistake a portrait for an actual person.

There is magic, right on stage, including some books that fly from a bookshelf and speak to us; a dexterous use of fireplaces as pieces of the wizarding transportation network; and an amusing wand fight in which a pair of wizards fling curses at each other. 

There are some creepy dementors that waft out over the audience, minus, at least from the upper seats, the cold draft that generally accompanies them.

At one point, what appeared to be a live owl flew across the stage (and on Tuesday seemed possibly not to end up where it was meant to be). We learn once and for all that Voldemort is pronounced with a silent T – “vol-DE-more.”

With a story by Rowling, John Tiffany and Jack Thorne, Cursed Child has been years in the making and is being presented as the eighth work in a series that had seemed closed with the last book.

It was odd to see the story unfold so vividly onstage when we are so used to approaching it first through the novels. 

Reading the Harry Potter books was for so long a rite of passage for so many children (OK, and adults), and the movies were always seen as faithful adaptations that didn’t introduce anything new to the plot. 

But audience members at the Palace Theater here could not have been more thrilled by what they saw. Many had traveled from far away for the chance to be among the first people to learn the thing that drives every fan in these situations: What happens next?

“It was even better than I thought it would be,” said Iman Khabl, 23, who had come from Edinburgh to see the play and who said she had been thrilled to find references to sometimes abstruse details from all seven books. 

“It was such a nice nudge to the fans, that they brought everyone back, that they kept our favorite characters while bringing in so many other things.”

The play attracted the usual complement of superfans, including groups of people dressed in Hogwarts robes purchased from the internet; people who had flown from California the day before and were being kept awake by little more than caffeine and hysteria; and a pair of newlyweds who ditched their honeymoon in Iceland for the chance to see the play.

Emily Trucks, 24, from St. Louis, was attending with her fiancé, Mike Wheeler, who is English. 

They met while they were exchange students in Florence and bonded over their love of Harry Potter and, in the case of Trucks, her love of Wheeler’s accent. 

“There were a bunch of us from St. Louis, and we had him read Harry Potter out loud to us,” Trucks said. “It was adorable.”

Rowling has done an excellent job of shrouding the production in suspense, letting out the occasional detail — Hermione is played by Noma Dumezweni, who is black; Albus is, basically, a disaffected youth — when it suits her. It’s hard to believe that further details will remain secret until opening night on July 30. (The play’s script, currently No. 1 on the Amazon pre-order list, will be released at 12:01 a.m. on July 31).

But for now, even fans lucky enough to procure tickets don’t know how Cursed Child ends. 

The play is in two parts, each a full-length play in itself. Only the first half was presented yesterday, and it ended on a truly shocking note of suspense. We won’t learn what happens until the first preview of the second part, on Thursday night. 

One thing we still aren’t sure of: Which character is in fact the cursed child? — The New York Times