LONDON — I did not actually see the heckler, but I can tell you what I heard from down the block: a man’s voice through what sounded like a megaphone, jeering at the crowd lined up outside the Gillian Lynne Theater for Andrew Lloyd Webber’s “Cinderella.”

This West End heckler was ridiculing us for two things, one petty — that we would spend money on tickets to such a show — the other poisonous.

Look at you in your masks, he said. What a bunch of fools.

Waiting on the sidewalk for my friend Ken — who was eager to see “Cinderella” because of the divided reviews, while I was curious because Emerald Fennell (“Promising Young Woman”) wrote the book — I was already double masked. I had landed at Heathrow only that morning and started my weeklong theater binge with a matinee of Nick Payne’s “Constellations.”

I felt guilty about the whole thing, really — about being in another country. But I’d had my two doses of the Moderna vaccine, I was a maniac about masks, and my world had gotten worryingly small in the pandemic. Months before, when I’d needed even the thinnest thread of hope that we would make our way through this mess, I’d bought tickets to see Ian McKellen play Hamlet. I didn’t want to give up that hope.

Though “Constellations” turned out to be disappointingly surface-skimming — with no chemistry between the stars, Chris O’Dowd and Anna Maxwell Martin, and thus too little humor and no heartbreak — it still felt like a miracle to step off a plane and a few hours later join that packed audience. (Because I was fully vaccinated in the United States, I didn’t have to quarantine.) Aside from the many masked faces in attendance, and the health questionnaire we had to answer in the 48 hours before the show to get our tickets by email, it felt very much like old times.

But at “Cinderella” that evening, I sat beside a barefaced tween, and two other unmasked children were next to her. All of them looked too young to be vaccinated. And, surprisingly, given Lloyd Webber’s public insistence that pandemic theater can and must be done safely, there was no vaccination or testing requirement for the audience. Plenty of people were unmasked, including those who removed their masks to eat or drink.

The musical itself, though? It was a messy, overstuffed pleasure, a Cinderella narrative so radically refashioned that we anti-princess feminist types finally, improbably, identify with her. Not incidentally, every solo that she sings is destined to be rapturously performed down the ages on high school stages.

And when, during the ball, the auditorium physically transforms so that we are sitting in the round, with the revolving stage so much closer to us that the scene suddenly feels intimate, it is an absolutely enchanting bit of theatrical magic — the kind you have to be there to experience.

The morning after, I headed to a Covid testing site. I’d been tested in New York two days before I flew here (a requirement scheduled to disappear for fully vaccinated travelers on Oct. 4, when regulations loosen), but people fully vaccinated in the United States also must get a test in the first couple of days after arriving. I went into a stall, swabbed the back of my throat (gag) and my nostrils (sneeze), then put the sample in a drop box.

I had more shows to see: first Kae Tempest’s “Paradise,” a reworking of Sophocles’ “Philoctetes” with an all-female cast at the National Theater. It was a matinee, and they were filming it; I spotted six cameras, including one that traveled slowly up and down a curved track in front of the stage.

I wasn’t sure I needed to see another telling of this story about the long-abandoned warrior with his festering wound, and Tempest’s script alone would not have persuaded me. But I did get to witness the enthralling Lesley Sharp, whose sinuous portrayal of the blustering Philoctetes had a crackling energy.

That night’s show was Tom Stoppard’s Olivier Award-winning “Leopoldstadt,” an intricate family saga inspired by the history of his own Jewish Czech family, some of whom fled the Nazis — as he, his parents and his brother were able to do when Stoppard was a toddler — and many of whom were murdered by them.

It was the third large-cast production I’d seen in two days, and the first to ask for proof of vaccination. This theater, too, was crowded, but behind my double mask it was easy to lose myself in the sheer Stoppardness of the play: the characters’ bristling intellectualism and the bourgeois ease that ebbs away, then vanishes completely when the Nazis show up.

My friend Ken and I went for an alfresco drink afterward, a stone’s throw from a couple of stage doors. It was heartening to see actors coming out of them, just as it had been sweet, on my walk to the theater, to spy little kids in ice-blue dresses on their way to “Frozen.” The liveliness felt so welcome, so necessary.

Early the next evening, striding briskly along the south bank of the Thames toward the National, I zigzagged through throngs of people of all ages having casual fun. It occurred to me, not for the first time, that in movies the characters racing through picturesque crowd scenes are often involved in a caper gone wrong. Which, though I didn’t know it yet, I was.

I got to the National 45 minutes early for Winsome Pinnock’s “Rockets and Blue Lights” because that was my assigned arrival time — staggered for pandemic safety. I’d already bought my program and a copy of the script when I sat down in a room off the lobby, checked my email and took a few stunned moments to fathom what I read. In big, bold letters, my Covid test result said “Positive.”

I fled on foot, double masked, straight back to my hotel, where I would have to isolate for the next 10 days. One of the first things I did was email all the box offices to tell them which performance I’d seen and where I had been sitting.

Before and after my test, and throughout my isolation, I felt completely well. But what about the unmasked girl next to me at “Cinderella”? What about the people around me at other shows? My friend Ken got tested and is fine. But how much good did my double masking do?

Theater is a social art form involving social risks. I calculated them before I traveled and decided they were worth it. But of course I didn’t realize I would be the menace in the room.

On the last page of the “Constellations” program is an airline ad aiming to entice theater lovers to cross the Atlantic again. “All the world’s a stage,” it reads beneath a close-up photograph of street signs — the intersection of Broadway and West 42nd Street — and above a shot of a theater interior that looks distinctly British.

In other words: Come on. You know you want to.

I had wanted to. I’m just not sure following that impulse was the right thing to do. Not yet.

AND THEN I WAS SPRUNG. At the end of the 10 days, I went to a kind, coincidentally musical-loving doctor (he thought “Six” might prove too British for Broadway), who examined me, declared me recovered and wrote a letter to that effect so I would be allowed to fly back to the United States.

But it would have been heartbreaking, and wasteful, to go home without getting what I came for. So I stayed to pack seven more shows into four more days, starting with McKellen’s hale and haunted Hamlet, a riveting interpretation in a frustratingly disjointed production.

I saw a matinee of the long-running ghost story “The Woman in Black,” which I’d hoped would have fresh energy post-shutdown (it did not), and, at the Menier Chocolate Factory that night, Rebecca Taichman’s superb production of Paula Vogel’s gorgeous “Indecent,” which both wrecked me and left me exhilarated. (Like many theaters, the Chocolate Factory has a lenient Covid exchange policy.)

I returned to the National to see Pinnock’s “Rockets and Blue Lights,” which I had read in isolation, and which in Miranda Cromwell’s staging takes tender and wonderfully theatrical care of Black bodies as it tells a brutal story of Britain’s history and legacy of slavery.

Then the director Ola Ince wowed me — first at the Royal Court with her excellent production of Aleshea Harris’s “Is God Is,” and the next afternoon at Shakespeare’s Globe with the best “Romeo and Juliet” I have ever seen: lively, love-struck and full of laughter, but with a postmodern awareness of the play’s sociopolitical resonances, and a million miles from romanticizing its suicides. The deaths at the end are horribly sad.

My last show was Bess Wohl’s odd, funny, terrifically cast new play “Camp Siegfried” at the Old Vic, the theater whose early-pandemic, livestreamed productions sustained so many of us from so far away. It was moving to see that beautiful space, cavernously empty on camera, fill up with an audience.

But at that and nearly every production I saw, there were loads — sometimes a majority — of barefaced people in the crowd, which felt reckless and delusional, as if the pandemic were a thing of the past. (I’d have thought an audience could at least unite in the cause of trying not to kill Ian McKellen with Covid, but apparently not.) If I hadn’t just had the virus, it would have freaked me out completely. New York theaters, vastly more rigorous about masks and vaccinations, feel much safer.

And yet. The other afternoon, I walked to the foot of Westminster Bridge to visit the statue of Mary Seacole, the British-Jamaican nurse I’d never heard of until two years ago, when Jackie Sibblies Drury’s magnificently kaleidoscopic play “Marys Seacole” made its debut at Lincoln Center Theater. My mind started whirring with thoughts of the Donmar Warehouse production coming up in the spring: how fascinating it would be to watch it with a British audience, how badly I want to do that.

I love London, love seeing theater here. I just wonder when it will feel OK to come back.