‘Stranger Things’ Creators The Duffer Brothers Address “Big Swing” Of [Spoiler]’s Return And Dr. Kay’s Motivations

SPOILER ALERT: This post contains spoilers for the entirety of Stranger Things Season 5 Volume 1.

One big question ahead of Season 5 of Stranger Things is answered in the fourth episode of the final season, now streaming on Netflix.

Viewers and fans have long debated over Season 2’s Kali (Linnea Berthelsen) and her place in the show’s story after her arrival and standalone episode “The Lost Sister.” She hadn’t returned to the narrative in Seasons 3 or 4.

Toward the end of Episode 4, “Sorcerer,” Eleven (Millie Bobby Brown) and Hopper (David Harbour) discover that Dr. Kay (Linda Hamilton) has captured none other than Kali, 008, Eleven’s “lost sister.”

“We’ve always wanted to bring her back because Linnea’s an incredible performer. We wanted to give her another chance to shine, but we talk about it every year, every season. We didn’t want to just put her in, to put her in,” Ross Duffer said. “We wanted her to have a real impact on the narrative and on Eleven’s journey. As we hit this final season, it felt wrong to not bring her back.”

Some felt that Kali’s episode in Season 2 distracted from the plot, and many wondered if it would be a one-off moment not to be revisited later. In Season 4, Henry mentioned that 008 had still been present at the time of a traumatic memory for Eleven, but Kali wasn’t present at the Massacre of Hawkins Lab.

“It would have felt like, ‘Oh, there was just this loose end or a mistake episode, and we didn’t want that. We didn’t feel like we could end the story of Stranger Things without bringing her back into the fold,” Ross continued. “As you get into the second volume, you really see how she fits into the narrative and Eleven’s journey, and she plays a really important role moving forward. Linnea’s awesome, so it’s definitely a big swing for this season, but one we’re excited about.”

From the discovery scene, it seems as though Kay and her crew have determined how to extract Kali’s powers and somehow transform them into the satellite technology they use to inhibit Eleven from using her own abilities. Hooked up to machines with a shaved head of her own, Kali opens her eyes to Eleven as they reconnect with no words said.

“It was really, really exciting. The Duffers don’t bring anyone back for no reason. [Kali]’s definitely utilized heavily within the season,” Brown told Deadline. “It’s really exciting because I don’t think Eleven has much family in her life, or at least people that entirely understand what she’s been through. One of those people honestly being Will, and not even Mike truly understands what she’s been through. So I think Will and Kali are the two people that know that trauma and so I think every scene I had with her felt more emotional and more intense than the rest.”

STRANGER THINGS. Millie Bobby Brown as Eleven in STRANGER THINGS. Cr. Courtesy of Netflix © 2025

Stranger Things has had no shortage of overbearing scientists and other figures who hope to harness the mysterious powers of Eleven and The Upside Down for their own nefarious reasons, from Dr. Brenner (Matthew Modine) to the Russians from Season 3 and 4.

Modine’s Dr. Martin Brenner is largely responsible for the 5-season story arc as the creator of Eleven and the catalyst for Henry Creel’s (Jamie Campbell Bower) growth into an all powerful being, aided by Eleven when she banished the first of Brenner’s experiments to another dimension, from which The Upside Down was born. Brenner, who was long thought dead as of Season 1, made his way back to Eleven in Season 4 before he met his end in Episode 8, appropriately titled “Papa.”

“We knew we needed a character to take over for Dr Brenner, because even though Matthew doesn’t want to admit that he’s dead, he is. He keeps putting out in the press, I think it’s really cute, that he might still be alive. No, but he is firmly dead. So we needed a replacement for him, and something we did, we’ve started doing this more as we went along, but we have done it before, which is working with our casting director, Carmen [Cuba], to find someone who we think would be really interesting in a role like that, before we’ve written that character.

Enter Dr. Kay who gives orders to the military like Lt. Colonel Jack Sullivan (Sherman Augustus) and his underlings. Her approach to the whole situation in Hawkins is very different than Brenner’s or even that of Dr. Sam Owens (Paul Reiser), who inherited Brenner’s mess from Seasons 2 through 4.

Linda Hamilton as Dr. Kay in ‘Stranger Things’ Season 5

Netflix

“Linda completely defined who that character was. We liked the idea that, and no offense to Paul Reiser or Matthew, but that she can kick some real ass. So she is brilliant, and she is a scientist, and she is a little unhinged, but she’s also physically dangerous,” Matt said. “She’s also dangerous in the sense that, unlike Papa, Matthew Modine, she has no emotional connection to Eleven. So as bad as he was to her, he still had paternal feelings for her. Linda, Dr. Kay, has none of those feelings. In that way, we think she’s aterrifying antagonist.”

Kay has set her sights on capturing Eleven, whom she blames for what is going on in Hawkins, but ultimately it doesn’t matter to Kay what Eleven’s — but really Vecna’s — intentions are .

“What’s interesting about Dr. Kay and Linda’s performance is that she’s not trying to solve a mystery here. Unlike Brenner, she has no understanding of what really happened with Henry in all this. What she sees is Eleven as a weapon, and that’s all she wants,” Ross added. “So these events are happening, but she’s not trying to figure it out, and I think that’s what makes her so scary. She’s just relentless in her pursuit of this one person in order to achieve her goal, which, as we move into Volume Two, we start to understand, really, what that goal is and why she wants Eleven so badly.”