She is surrounded by a small crowd on a street corner in Manhattan's Lower East Side. A photographer snaps pictures and spouts compliments: "Beautiful, perfect." Tourists stop to take pictures of their own. Her mother stands nearby holding a sandwich and fries, which she snacks on between shots.

She is in full makeup, with professionally and perfectly styled hair—she spent two hours in "glam" before her GQ photo shoot. She leans in toward the camera, making the faces models make. She bends her knee and pops a leg in the air. It's a very skinny leg. And actually, now that you see her standing next to the photographer, she's very short. Just over four feet tall. She is Millie Bobbie Brown, the very adult 12-year-old star of Netflix's out-of-nowhere hit Stranger Things.

Brown has the poise, if not the height, of an acting veteran. But sometimes the childishness can't help but bubble up, because, you know, she's literally a child. The professional, for instance, might explain how she has mixed feelings about Sea World's treatment of animals. The kid, however, will tell you this story: "We went to, like, a park together, and then I hyperventilated, and my friend's sister passed out."

For anyone who hasn't seen the show yet: After a close friend disappears, Dungeons & Dragons–playing nerds find and befriend a borderline-mute girl with a shaved head and superpowers—that would be Brown—who escaped from a mysterious government facility nearby. Like a new group of Goonies, they head out to find him, fall off their bikes quite a few times, and eventually piece together that their friend is trapped in an alternative world. And their new bald buddy is the only hope of getting him back. If it sounds weird, that's because it is.

For the boys on the show, most of whom are newer to acting than Brown, she's a tether to propriety. "They're crazy," Brown says later. "I keep them in check."

Steven Pan

At least some of Brown's perceived gentility comes from the accent. The actress was born in Spain to English parents and lived in southern England before moving to Orlando, then Los Angeles. She has the voice of someone who enjoys a crumpet—the voice of someone who says, "I am a really great daughter. Mum, am I a good daughter? Mummy?" (Her mom confirms that she is.) "My family is really proper," she says. Her dad, sitting just behind her, interrupts with a Cockney accent, "Ah you kiddin' me?" "Some parts of it," Brown concedes. "My brother's really well-spoken."

She sounds more like her brother than she does her father. (See: Brown the professional.) But the poshness doesn't always last long. Once she starts speaking about something she's actually interested in, it stops feeling like she's making sure her good side is properly framed in camera 2. Like when she talks about making a cake at Duff's Cake Mix in L.A. with her friend Maddie (Ziegler, the one you've seen dancing in Sia music videos). Her eyes go wide, and she stops taking breaths between sentences. "We made a Minions cake," she says. "It was really good, but Maddie was very controlling over it. I wanted to help, but I mostly just sat there and watched. I did eat most of it. My sister ate most of it. So I sat there. I looked around and started to talk to everyone. I'm more of a, like, a...she's more, you know, detailed. I'm just like, 'It's a minion.' " Uh-huh.

The day we meet, Brown isn't feeling so well. It might be the stress of her schedule (this interview is being squeezed in between a trip to the White House to meet President Obama and the start of the season 2 shoot in Atlanta). It can't be from memorizing lines, because her character barely had any, stealing scenes with subtle shifts of her eyes and intense looks of silent terror rather than lengthy monologues. But her ailment doesn't seem to be bothering her right now. She drinks a can of Coke and plows through the available snacks, which makes her feel guilty. "I ate all the guacamole, and I don't feel good about it," she says, before finding the bright side of her snacking. "You know, guacamole is really healthy. It's really good for your skin."

She's ready for another lesson: Muay Thai boxing, which she does every day. Despite the pleas of her publicist, who reminds her that she's been feeling sick—a concern Brown responds to by completely ignoring—we're up from the table, and one of us is ready to spar. Her face corkscrews in concentration.

"Hands up. All the way up. Protect your chin."

She's a patient teacher. And focused. She makes a tss sound through her tongue and her teeth with every punch. "Make sure it comes from your diaphragm. And you gotta bounce." Apparently I don't bounce enough. "Bounce! Bounce!" she repeats. "Now jab, jab. One-two!" She pops off a left hook and two quick jabs to my body, with a strength that indicates I should possibly take up martial arts, or at least cross the street if I ever run into her again. We high-five. She grabs my recorder: "Ya done it."