[Editor's note: The following contains spoilers through the series finale of Mare of Easttown, "Sacrament."]

The Mare of Easttown series finale was an emotionally devastating affair, but viewers who have been along for the ride didn’t expect anything different. The HBO limited series has been wildly emotional through all seven episodes, as we traced detective Mare Sheehan’s (Kate Winslet) dogged investigation into the murder of a young girl named Erin (Cailee Spaeny) throughout the Philadelphia suburbs. But in contrast to some other murder mysteries, creator Brad Ingelsby’s approach to Mare of Easttown painted a full-bodied portrait of the characters living within the titular town, to the point that we as audience members empathized deeply with their struggles, hopes, and despair.

That was true right down to Episode 7, in which it was revealed that Lori (Julianne Nicholson) and John’s (Joe Tippett) son Ryan (Cameron Mann) is the one who killed Erin on that fateful night. Having discovered his father was the real father of Erin’s baby and wanting to keep his family intact (especially after what happened the last time his father had an affair), Ryan confronted Erin with a gun in an effort to scare her, but ended up accidentally shooting and killing her. John and his brother Billy (Robbie Tann) subsequently cleaned up and moving Erin’s body to cover for Ryan, and when Lori was later told that Ryan was the killer in Episode 6, she agreed to keep the truth from her best friend Mare.

But Mare figured it out, and the Mare of Easttown finale saw some dramatic, incredibly emotional confrontations between Mare and Lori over Mare’s decision to take Lori’s son away from her. Nicholson and Winslet delivered phenomenal performances in these scenes, so I was thrilled to speak with Nicholson by phone recently about her work in the finale and in the series overall.

During our conversation, Nicholson revealed when she found out Ryan was the killer, and talked about how she and Winslet approached their tense scenes together in the finale. She also discussed how the COVID shutdown impacted production, and what it was like filming the series out of sequence (they shot one of the big finale scenes in the first month of production). Nicholson also talked about Lori’s decision to keep baby DJ, and how she also thought Lori might be the killer as she was reading the script for Episode 7.

Check out the full interview below once you’ve had time to process your emotions from that excellent finale.

Collider: When did you find out that Ryan was the killer?

JULIANNE NICHOLSON: So I can't remember exactly, but I think I read up to Episode 6 before saying, "Yes, I'd love to be a part of it." And I had been told a little bit about Episode 7, but not the facts of who had done it. But then before we started filming, I did know where it was going. But Episode 7 was like a big deal. It was kept under lock and key. They were always sort of referencing Episode 7, who had 7, who had read 7, so it was very important to keep the secret as long as we kept.

So you were kind of brought in on it whenever it was time to shoot that episode?

NICHOLSON: Well, I was told early on, so I knew from the beginning. And I think Joe [Tippett], who plays John, and Robbie [Tan] who plays Billy, I think they were told too, because it's important for them to know what they've been up to. It informs everything. Nothing you need to reveal it or give it away, but just for your own choices that you're going to make.

There were certainly vibes of like, "it's very clear that Lori is protective of her family." Did you see on Twitter that a lot of people were kind of thinking you were the top suspect, leading into the finale?

NICHOLSON: Yes, I thought that too when I was reading Episode 7, because I had already agreed to do the job. And then for some reason, it really bummed me out, the idea of if Lori was the killer. I was like, "Oh God." I mean it was terrible, terrible that it was her son, but I was sort of relieved that it wasn't her. I guess I wish it was Lori so then her son didn't have to suffer and she didn’t have to suffer the heartbreak of her son's suffering.

I thought it was Lori going into it. And I was like, "Yeah, it makes sense from a plot perspective and everything.” But while this has been a murder mystery show, when it's revealed that it's Ryan, it really kind of brings it full circle, that this is a story about parents and children, and kind of the lengths to which parents will go to protect their children, and how they feel when they feel like they've failed, when something goes wrong. Was that something Craig [Zobel] and Brad were stressing?

NICHOLSON: I think so, yes. I think, yeah. About, as you say, that the crime was sort of the cherry on top, but the story is this place, these people, these friendships, family, and yeah, parenting. I think that was something they were all very conscious of as we went.

I wanted to ask you about the scene between Lori and Mare in the car in the finale, which is really devastating. I think you and Kate are both just really tremendous in that scene. I was wondering how you guys both approached playing that out.

NICHOLSON: Thank you. We actually shot that pretty early on, that scene. I think month one of filming, because we shot all the seven episodes as one piece. So that was kind of crazy. I think we came to it with our own ideas, but knowing the depth of loss that would take place if these two couldn't be in each other's lives anymore. I think we did that last up on a Friday night. It was brutally cold, and we just kind of kept our distance from each other. And then we tried it, and then we just did it a number of times. I don't think we had to do it that many times.

Actually, now that I’m remembering, I think one of the times between takes we hugged, which was very helpful and moving, to have that connection with her. I've known Kate for a long time, and I've always been a fan of hers as an actor. And so we kind of didn't talk much about it on that night, and we just filmed a bunch of times and knew the stakes.

What's so devastating about it is that you really empathize with Lori in that moment. And I think Kate leading up to that, you can see in Mare, she knows she's making a decision to take someone's son away from them, just like she had lost her son. I mean, it's a terrible crime, of course, but it's hard not to understand where Lori is coming from.

NICHOLSON: I agree. I feel like John's going to take the blame. Give it to him, it's his fault anyway! Leave Ryan alone!

Of course, let the guy take responsibility for starting this mess!

NICHOLSON: Exactly, if you're going to be planting heroin on your grandchild's mom, then who are we?

That's true. That's a fair point. You wait until now when it's someone else’s life to do the right thing.

NICHOLSON: (Laughs) Yeah, but I get where she's coming from. But I think that Lori would have been very happy for John to take the fall and just move on.

I assume you guys block-shot this, but I know it was also interrupted by COVID. So was that a little disorienting? Or did you shoot all of your scenes before they had to come back for after the COVID break?

NICHOLSON: No, no. Yeah, we went back and forth and back and forth. It was odd to have that break and come back. But I think at least for us, it was helpful. I think we filmed for at least four months. So at least we all had these characters in our skin. We have these relationships to sort of return to, as opposed to create from nothing. I think that would have been more challenging.

And so it was odd. I remember my first scene back, we had to do a reshoot of the bar scene. And so suddenly I was like having literally not stepped foot outside of my house for six months, I was suddenly in a bar with a bunch of background talents and we all take our masks off, not far from each other. And of course everybody was tested and had quarantined for a couple of days, but it was still like, "Oh." And then the scenes became more intimate again, and it would just be one or two people and a lot of them were outside. I mean, this production was amazing how they took the COVID protocols and just kept going. I can't imagine the headaches, the details, the rescheduling that went on in other offices. Whereas I'm in my trailer, eating snacks, like, "when do you need me?" (laughs)

So when did you shoot your final scene with Kate? The one that ends the series.

NICHOLSON; That was before... I believe that was pre-pandemic.

Wow. Because there's such a sense of finality to it and that just feels like a really beautiful moment. It's crazy to think you shot out of sequence.

NICHOLSON: Yeah, I know. I know, but I'm pretty sure that was before the shutdown. The good thing was that they had all this time to edit. All the time to sort of streamline. I guess that's probably a good thing and a bad thing for the editor. But yeah, I think they spent a lot of time editing over the break and sort of figured out what they needed when we came back and what they didn’t.

The physical performances between you and Kate in that scene, I think is really fantastic. What were the conversations that went into that? Because there’s not a lot of dialogue. It’s all communication through body language.

NICHOLSON: That's Brad. I mean, Brad, the writer, and Craig, the director. I think we played it as it was written. Really. I love when she comes in, and I don't know exactly how much time has passed, but I think a couple of months anyway, and they hadn't spoken and Lori's been dealing with the fallout of all these things that you mentioned. There's no "hello" even, I think it's just, "you want some tea.” I love that entry into that scene. You don't know where it's going to end by the way it starts. And I think we both knew what was on the line for these women and this friendship and just explored that. I love Brad's confidence in silence. He'd done enough in the run-up to that scene to not need it to be about words. That's a special writer. That's a brave writer. He trusts everything that he's already created up until that point. And it's a good feeling too, to know that someone trusts you in that way.

That's what I was going to say. That's a lot of trust in you to really have those characters down and know exactly what to do, and I think it just ends it all on a perfect note.

NICHOLSON: Yeah, I'm so glad. Thank you.

That’s kind of the thing that's really striking about this series is from the very first episode, which is really kind of a day in the life, what I really enjoyed about it is that you really get a sense of who all these people are, really kind of in their bones, to the point that when Erin dies at the end, it's not like, "oh, that's the victim." You're in tears because you grew to love this person over a span of just one hour. Was that prevalent on set among the actors? That they felt like, "oh, all of these characters are really kind of get getting rich, interior lives."

NICHOLSON: Yes. But I also do think that something happened from filming it. Yes, we did feel that there was a real ease to being together. Always, for me, with the people that I acted with, and the crew, and the director, and Brad. So it was never high stress. And with Kate, it was very important to her for this to be as authentic and grounded as possible. But I do think that sometimes something happens from filming to when it's edited, for how it's filmed, how it's edited to the music, to everything. And so something extra special happened with this, from the ease and the loveliness with which we actually did the scenes, to then what it becomes. I think something happens sometimes, and luckily it did here.

I'm curious, in your mind — why do you think Lori chose to keep DJ herself?

NICHOLSON: I think Lori is a good person, and she wants to do the right thing. And what's going to happen to this kid if she doesn't take him? The half-brother to her children. I think it would be harder for her to live with that going forward, not taking him in, than taking him in and all that that brings up for her.

That makes sense, yeah. Although when I thought you were the killer, I was a little worried when you were alone with the baby.

NICHOLSON: (Laughs) Yeah, I can see how that could be alarming.

Because you knew something was going on. Because Lori knew what had happened, and she's turning things over in her head, so she looks a little shifty.

NICHOLSON: Yeah, good. But it's still fun, isn't it? To even have those ideas placed in your head, have a show where you just don't know, where anything could happen and anything seems possible. So exciting.

Well, and that's what I'm saying is that it's a testament to the writing that what I thought was wrong, but your performance is still correct. It's still like, "Oh, now it all makes perfect sense." She knows what happened to Erin, and she knows it was her son's fault, and she has to cover it. It just all tracks versus like, "Oh, I guess that's it."

NICHOLSON: That's Brad. When I look back at all of the little side avenues, he had so much. I read something that was talking about the gun that was placed in the fishing box. I remember conversations about that early on. Nothing's by accident. And I can't begin to imagine how a mind actually creates all those little details because it's like, "Okay, we don't want the audience to know who puts the gun in there." Is Billy seeing it any surprise? Are you seeing it with recognition? It can be any number of things. And also Brad wrote and Craig, as directed, was like, "Okay, we'll film it like this, but we'd also like to have a version where maybe if people go back, it's something they wouldn't notice with a first viewing. But if you go back for a second viewing, there might be things that act as little tells." And so it's like you get a different experience watching it a second time. I thought that was kind of cool.

I do remember Ryan gives a look in episode five or six, and I was like, "That kid knows something. Something's going on."

NICHOLSON: (Laughs) I did see that around, like, "What's up with Ryan? Why did they keep doing these lingering shots? And why did he beat the shit out of that kid at school? And..." But I love that there's always like, "Yeah, but it could be this, but it could be this, but it could be this."

You said that you knew Kate before this, but again, I was really struck by the dynamic between you and Kate and also just the women at the beginning of the series. How did you guys go about creating that kind of comradery among the characters? Because it feels so authentic, that like, "Oh, of course, these people have known each other since high school."

NICHOLSON: Right. Well, Kate and I have known each other for many years, so to have that inbuilt history is invaluable. It's something that you just can't fake. So that was part of, I'm sure, why she was hoping that I would do it and part of why I wanted to do it, was having that relationship in place. And then the set and Kate... A lot of it starts at the top. It's the ease or it's the vibe that number one on the call sheet is spreading around. People follow by example. Also Jean Smart is the easiest, most laid back, hilarious person you've ever met. So just upon meeting her, you feel like you've known her forever.

She's so good on the show too.

NICHOLSON: She's so good. Have you watched Hacks?

Yes, she's amazing in Hacks.

NICHOLSON: I just started it. She's so amazing. She's just awesome. So, I think it was casting. I think it was just the feeling of everybody just there and knowing the importance of it and taking it seriously, but doing that in a rather relaxed way.

All episodes of Mare of Easttown are now streaming on HBO Max.