Hawkins’ courageous crew of misfits has a mysterious new member.

Meet Max, the steely, sardonic tomboy who skateboards into a haunted Indiana town in the second season of Netflix’s Stranger Things (streaming Friday). With her badass exterior and high scores as arcade gamer “Mad Max,” she captures the attention of middle-schoolers Dustin (Gaten Matarazzo), Lucas (Caleb McLaughlin), Will (Noah Schnapp) and Mike (Finn Wolfhard), who reluctantly welcome her into their circle after losing Eleven (Millie Bobby Brown) to the Upside Down.

Max is played by 15-year-old Sadie Sink, a five-year Broadway veteran (Annie) whose film and TV credits include The Glass Castle, The Americans and Unbreakable Kimmy Schmidt. The actress first watched the Netflix series just a few days before her audition last year, which entailed a series of top-secret callbacks and screen tests over the course of three weeks.

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“I knew it was (Stranger Things), but the scripts I was supposed to perform for the audition were altered, so that a scene I would have with Lucas would have a code name instead of using his actual character’s name,” Sink says. “I was given this very small amount of information about what the character’s like — she’s a tomboy, she skateboards — and that’s pretty much all I knew for a long time.”

After auditioning hundreds of girls for the role, “Sadie was a bit of a no-brainer,” says writer/director Matt Duffer, who co-created the show with his twin brother, Ross. “We read her with Gaten and Caleb, and there seemed to be innocent, child chemistry.” Plus, she already knew both actors, who also got their starts in New York theater: “Apparently, all Broadway kids play in the same playground. We could totally do a musical episode, if we’re so inclined. All of our kids can sing.”

At first cagey and highly skeptical of the creepy happenings in Hawkins, Max eventually gets candid with her young pals, revealing why her family moved to town and the complicated relationship she has with her callous stepbrother, Billy (Dacre Montgomery).

“I like how she's incredibly tough in terms of putting up with her brother and also very closed off, which was fun at the beginning,” Sink says. “It made the moment when she opens up a little more special.”

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Before Stranger Things, Sink’s knowledge of 1980s pop culture didn’t stretch beyond music and fashion. She has yet to see Mad Max, her character’s namesake, and has watched only one clip from Indiana Jones and the Temple of Doom, which the show pays homage to when Max drives a car, placing a block under her foot so she can reach the gas pedal.

The high-stakes scene was Sink’s favorite, as Max speeds down a rural road shouting at all her friends. Although “sadly, I did not do any actual driving,” she says. “I'm in driver's ed right now, so I can tell my teacher, ‘Well hey, I've got some driving experience on camera!’ ”

Other on-set firsts included skateboarding, which she spent a month learning, and kissing a co-star, after a season-long love triangle between Max and two of the boys.

“Not everybody has their first kiss in front of 200 extras and their mom. That's the part about it that sucked,” Sink says. “Because the camera was circling us, we had to do it like 10 or 12 times. After a while, it was like, ‘Alright, OK, we get it.’ ”