Spoiler Alert: Do not read if you haven’t watched “The Piggyback,” the final episode of “Stranger Things 4,” now streaming on Netflix.

Season 4 of “Stranger Things” ends on the show’s most bittersweet note yet, with the crew barely managing to scrape together a (seemingly temporary) victory against main villain Vecna (Jamie Campbell Bower) in their quest to save Hawkins, Ind. from the Upside Down. Over the course of the epic two-and-a-half hour finale, many of the characters go through hell during their multi-step plan to kill Vecna, with Eddie (Joseph Quinn) dying a heroic death, and Steve (Joe Keery), Nancy (Natalia Dyer) and Robin (Maya Hawke) nearly being choked to death by the vines of the Upside Down.

Even in a particularly grim finale, Lucas’ (Caleb McLaughlin) storyline stands out as one of the most grueling. Assigned to protect his ex-girlfriend Max (Sadie Sink) as she willingly offers herself up as bait to lure Vecna into her mind, Lucas keeps the mood light at first, asking Max out for a movie date via notepad communication. But things quickly veer off plan when Lucas is confronted by Jason (Mason Dye), the crazed leader of the Hawkins High basketball team who’s convinced our heroes are a cult attempting to spread Satanic influence throughout the town.

In their resulting fight, Max’s walkman — containing Kate Bush’s “Running Up That Hill,” the only thing that can pull her out of Vecna’s trance — is destroyed, and the paranormal serial killer critically injures and almost successfully kills her off, to Lucas’ horror. In the final leg of the finale, Lucas desperately clings to Max and begs for her to stay alive — giving McLaughlin, who has portrayed Lucas since he was 13, the biggest acting showcase he’s ever had during his time on the show.

Shortly after the finale premiered, Variety spoke to McLaughlin about shooting Lucas’ reaction to Max’s death (until Millie Bobby Brown’s Eleven brings her back to life), developing his onscreen chemistry with Sink and where the character’s storyline will take him during the fifth and final season.

Lucas’ arc this season is about him really trying to fit in at school, and finally get popular. I’m curious, what do you think it is about Lucas that he’s the person in this friend group who was really pushing for social acceptance?

I feel like everyone has their own paths, and Lucas chose the path of trying to do something different and find some type of peace in his life. And I feel what motivated him more was his relationship with Max. I feel like in the time of Billy [Dacre Montgomery], her brother, dying, she kind of ran away from Lucas. And I felt like he found his peace and happiness through her and his friends. So when she distanced herself, he was like, “Wait, I gave all my energy and love to her. So I need to find something else.” Maybe he wanted to impress her. And on top of that, he was just tired of being bullied. He was tired of being called names and being a nerd. He wanted to be cool. So I would understand why Lucas would want to look for something new, and something different to find some type of peace.

While I was watching the season, I wondered whether Lucas’s desire to end the bullying he’s dealt with has anything to do with him being the only Black kid in this friend group, and one of the only Black students at the school in general. Do you think that plays any part in his arc this season?

I recently rewatched the series myself, and I look back at Season 1, one of the bullies was calling him “Midnight.” Like, he made fun of his skin complexion. Back in the 80s, Black kids definitely got bullied for being Black, especially in a predominantly white school. So I think that definitely played a big part. He probably got bullied more than the other kids in the show. We’re not gonna play on that, but it probably had to do something with it. His friends were there for him, they love him, they’ve been best friends for life, but they probably don’t know how Lucas feels inside. Definitely, silently, that plays a part.

In the finale, there’s a scene in which Vecna impersonates Lucas in Max’s vision. How’d you approach playing Vecna in that brief moment?

People always ask me, “You probably rehearsed that last episode a lot.” To be honest with you, I didn’t. I don’t like rehearsing much, depending on the scene. I like to understand the moment and the feeling of where I’m at. Because I already know how to play Lucas, right? With Vecna, my thought process was like, “OK, Vecna is trying to disguise himself as Lucas. I’m going to just be Lucas, but a more menacing, stranger, more aggressive Lucas.” I knew I wanted to have a tear coming down my face, so I knew in my head where I am in the scene. “How do I make Max scared, how do I make Sadie scared?” I didn’t tell her what I was going to do, I didn’t rehearse it — I just went for it. Of course, as takes went on, I got better with each take, but I don’t usually like rehearing because that throws me off. When I rehearse too much, it doesn’t come off natural.

Later in the episode, you have fight scene with Mason Dye. I’m assuming you had to rehearse that fight?

Yeah, that took two or three fight rehearsals with Mason. I give it up to any stunt person that does fighting scenes. Stunts. Are. Tiring. You have to breathe, and get fake hit, and punch and fall to the ground. It definitely took a lot out of me. It was funny, we would have moments in the fight, Mason and I, were we would laugh, or if I would get hit I would make a funny sound. I definitely remember we improvised one part where you see Sadie in a trance, Vecna’s got her, and we’re in the back and he’s gut punching me. We choreographed one little sequence where he did that. And he’s just like, “All right, I’m gonna punch you like, 10 times, and then we’re gonna do an uppercut.” And I was like, “All right, cool.” So we’re over here just going “Uh! Uh! Uh! Uh!” until they call cut. And Sadie started laughing, and me and Mason were laughing and they’re just like “What is happening?” But it came out well; it looks really good.

The scene when Max dies — that’s such a showcase for you. What was it like tapping into that really emotional reaction for Lucas?

I wouldn’t say it’s about the tears, because since I was six years old, I used to cry at lunch tables — I used to do it for fun. I’d be like “Watch me cry!” and I used to do that in front of my friends. I have tears built up in the back of my eyes right now, and I can go. I just need a lot of water and I’m good.

But once I got into it, I just started thinking sad thoughts, and I went for it. I knew the situation, and I knew how I was feeling. Sadie’s performance, she definitely was giving me the engine to really bring it there. One thing that really got me was when Sadie said “I don’t want to die.” That moment, I was like “Whoa, this is really happening.” At one moment, when I was recording, I remember feeling like there was no one else in the room. There were no cameras, it was just Sadie and I, and she was pleading for me to help her. And I was just like, “There’s nothing I can do.” I wanted to feel helpless, because that’s how Lucas felt in that moment: helpless. But also I wanted to save her, so it was more than a helpless moment, you know? It was a lot going through my mind, but I just went for it. As long as I know the feeling and the space I’m in, I’m able to to do it. I try not to think too hard. Once I know the feeling, I’m good.

In the scene you scream for Erica to help as Max is dying. The “Stranger Things” writers’ room Twitter account tweeted that that was an improvisation. Is it common for you to improvise on set during those emotional scenes?

Yeah, in all of “Stranger Things,” if I have a line or scene I really try to improvise, I’ll ask the Duffers. They’re pretty open to me improvising and saying what I want. For this scene, they just said “How are you going to play it?” And I was like, “I’m gonna really just go for it.” They were like “All right, do your thing.” I had lines, but I improvised around them, because if I’m going with the lines, it’s not going to be natural. And that “Erica, help!” was because I know, and the audience knows, that Lucas would never ask for his sister’s help. But in the moment, he’s so helpless, he needed his sister at that moment, he needed someone to be there with him.

What was it like on set shooting the scene when Max levitates and her bones crack? Did you have a visual reference for what was going on while you were shooting?

I had to ask them what I’m looking at, and they said, “So you’re gonna see her bones cracking.” I never saw how that looked on set, so I had to envision something crazy, because I wasn’t able to get a visual until the premiere of the show this year.

You and Sadie Sink have been working together since you were about 14 or 15 years old. How has your approach to playing Max and Lucas changed as you’ve gotten older?

I’ve known her since I was 10 years old. We were on Broadway in different shows [McLaughlin was in “The Lion King,” Sink was in “Annie”], and we used to see each other in Times Square at this park that all these Broadway kids used to go to. So we knew each other before “Stranger Things.” Max and Lucas, they started off as friends, so their relationship is very genuine, and you can see that this season. They’re really there for each other. I feel that because of Sadie and I’s friendship, it’s easy to just have that same type of relationship on the show. As actors, you just go with the flow. Me and Sadie never really talk about it, we kind of just go for it, the chemistry has always been there. Once we’re on set there’s nothing to talk about, it’s just showing that connection and just being actors.

I’m sure you you don’t know anything about what’s going to happen in the final season. But is there anything you want to see happen for Lucas?

Personally, I would love to see Lucas have a revenge arc this season. You’ve really seen him go through something, and I would love for him to kind of have a chip on his shoulder.

Nice. Personally, after everything, I really think he and Max deserve that movie date.

Exactly. But where we left off Lucas, I don’t think he’s gonna be jumping into Season 5 doing jumping jacks, jumping in the air like, “Yeah, I’m all good! It’s ‘Stranger Things!'”

This interview has been edited and condensed.