SPOILER ALERT: Do not read if you have not watched the first four episodes of “I Know What You Did Last Summer,” streaming now on Amazon Prime Video.

“I Know What You Did Last Summer” as a franchise has its roots in Lois Duncan’s 1973 novel about a group of teenagers who hit someone with a car, cover it up and then are stalked and murdered for the secret one year later. But it rose to popularity with a new generation in 1997 when Jennifer Love Hewitt starred in a series of film adaptations. Nearly a quarter-century later, the story has been adapted once again, this time as a dramatic television series for Amazon Prime Video, with Madison Iseman as the new face of the franchise.

Iseman stars as twins Alison and Lennon in the new series — recent high school graduates who really only have the same face in common.

“It’s on every actor’s bucket list, I feel like, to play twins,” Iseman tells Variety. “It was definitely a challenge, but it was one I was up for.”

Lennon is the more popular but also wilder and more manipulative sister who sleeps with the guy (Dylan, played by Ezekiel Goodman) Alison likes after advising her sister to let loose more. Although Alison learns about that betrayal first, it pales in comparison to learning Lennon also set up an OnlyFans account, posting pornography under her sister’s name.

There is a sense of irony in Lennon masquerading as Alison on the internet, though, because after their graduation party, Alison assumes Lennon’s identity.

In a more personal twist on the source material’s premise, when the teenagers hit someone on a dark and winding road in this version of the story, it is Alison at the wheel and Lennon in the street — only everyone assumes the opposite, and Alison allows that to happen. The group dumps Lennon’s body in the water and heads home. Alison confides the truth to her father and then goes off to college under her sister’s name.

A year later, she returns to her hometown and reunites with those with whom she shares a terrible secret, who are now being targeted by a murderer to face the consequences.

Here, Iseman talks to Variety about distinguishing between Alison and Lennon, as well as her approach to learning information about the killer and which death is her favorite of the season.

Take us back to the audition for this show. Did you have to read as both sisters right off the bat?

Originally the first call of seeing people, they only had us read for Lennon, which I thought was interesting. But I just did the extra credit and I was like, “I’m just going to put on the other sister.” I was sure they were watching a lot of tapes, but I’m always down for extra credit!

How much influence did you have in creating nuances to differentiate the two sisters, especially in the beginning when the majority of the scenes they shared had them looking identically?

It was a pretty interesting process. When we finally got to Hawai’i [to film], it was a lot of conversations with Sara [Goodman, showrunner] to figure out who we wanted these girls to be, both as separate people and together. It got tricky because the first time you meet these girls is at this grad party where there’s so much going on and part of the big twist in the pilot episode is that they both have to end up looking identical — in the same outfit, with the same makeup. Normally when you approach twins, it’s so great to have physical differences in how they style their hair, how they do their makeup. We weren’t allowed to have that, so because of that, it was so important to really get to know who they were, even from when they were younger. So I did a lot of journaling. I really tried to make them have their own life beyond what you guys see in the show. They are so different — they carry themselves so differently — but I wanted them to have similarities and feel like sisters and share pieces of each other.

How did it work in production in terms of planning and playing out scenes where you were acting opposite yourself? Were you always able to do all of one character’s coverage in a row before switching to the other, or did you have to toggle back and forth between headspaces in a close amount of time?

I would usually start with Lennon because as a person she pretty much drives every conversation, so that felt more natural. And then we would switch halfway through the day and fall into Alison. There was one scene I did with Zeke with both the twins and he wanted me to do both for him while I was off camera, so I was jumping from one side of the camera to the other. It was so silly, but it worked.

The technicality of it was all brand new to me. I knew it was going to be double the work of everything, but even just a normal scene, the special effects team has to be there, so it was a whole new way of working. One of my favorite parts of being a performer is doing so much work beforehand and then showing up on the day and letting everything go and just being present in the moment with your scene partner, but for this, because my acting double was basically mimicking everything I had pre-planned, it was a whole process of rehearsals and pre-planning everything down to, “What is my reaction here? How do I respond?” That was more time consuming.

When you’re in a live scene with yourself, we know you have your stand-in there for eyeline or to catch the back of her in an over-the-shoulder shot. How did the scene in the water when Lennon’s body rose up work?

We played around with a lot of different ways to pull it off because I think you really never know until you get to the editing room how it’s going to work. But they ended up going with face replacement, which I think was the only time they ever used face replacement. It was my double gracefully floating in the water.

How much do you feel Alison is changed by having to pretend to be her sister? Is anything she’s doing seeping in and being adopted more permanently than she may even want to acknowledge?

I really am, in a way, playing three characters in the show. Alison as Lennon is different. But at the same time, she knows Lennon like the back of her hand; she’s been in her shadow all of her life; and I think deep, deep, deep down there is a part of her that always wished she could be her. But when the reality hits that night and she comes home and has that moment with her dad, that’s releasing, and then she runs away — she goes off to college and she leaves it all behind — and I think there’s a part of her that hopes that somehow in the year, everyone will just forget. Obviously that’s not going to happen, but that’s how Alison has always dealt with complicated situations — she flees; she doesn’t want to deal with it. When she comes back and she’s forced to, especially because there’s the element of someone stalking the kids, that’s the first time I think you’re watching her actually sit in what she started. And all these new revelations come, like with the OnlyFans account, and she’s learning her sister was way worse than the image she had of her. And then she’s dealing with not wanting to be her anymore — “Can I quit?” It was really a tug-of-war on set for scenes between Alison and Lennon. Sara and I talked a lot about how much to forget, how much to forgive, how much to give back.

Let’s go back to her time away for a second. In your mind, who was she in college? Did she get to be herself, just under her sister’s name?

She went in as Lennon and I think she was able to take the parts of Lennon that she wanted to be, but also she could reinvent someone completely new. She went off to college and she stopped texting Margot back, she forgot everything because she was able to create a world for herself for once.

Early on in the season, characters speculate that Lennon wasn’t really dead when she was thrown in the water and so maybe she’s the one stalking and killing now, out for revenge. Obviously if that were true it would have greatly affected your performance, so how did you approach how much information to ask for about who it was?

We all wanted to know very badly! And Sara is the best secret-keeper on the planet. We all got the first four episodes before we came to Hawai’i and I think Brianne [Tju] made a Venn diagram, trying to figure who the heck it could possibly be. And we were all wrong except for one person. I swore I knew who it was! But it adds to it because our characters are just as confused as we are. In a normal scene, if we did know what was happening at the end, you’d have to shut that part of your brain off, but we didn’t have to worry about that.

When you eventually found out who it was, did it all click together or did it leave more questions for a potential second season?

I think a little bit of both. For me it was a shock, but then I went back and looked at it and the pieces are all there. What’s so great about it is it’s not a let-down and they’re not trying to hide it from you. If you were to sit down and analyze every single episode, you could figure it out. There’s definitely a bunch of misleads, but it’s there — it’s just hidden in the craziness of our show.

And when it’s revealed that it’s absolutely not Lennon, now part of the secret is out because now everyone knows she is dead. Is this a moment where some of the stress and weight is relieved both for you as a performer juggling a lot of complex elements, but also for Alison, who has been holding in so much?

I think there’s a piece of Alison that almost wishes she was alive. She’s still family. But at the same time I think it is a huge relief. She was so clear in the beginning that she knew it was not her sister, but everyone else got in her head and made her think it possibly was. So I think, if anything, it was just a feeling of being right, and that always feels good because so much of the show is everyone not necessarily gaslighting each other but trying to convince everyone, “No, I saw this, this happened, this happened” and everyone feels like they can’t trust anyone. So if anything, this was a moment of, “I was right” and she can go from there.

With everyone pulled apart by their own fears and levels of guilt and confusion, and the fact that Alison is back as someone else, is there anyone she can get genuinely close to? 

I think the whole time she’s going back and forth between loving who she was as Alison and loving who she is as Lennon. And in the episode with the funeral, she has this moment where she apologizes to Margot, and in my head, it was really Alison apologizing on behalf of her sister for everything her sister’s ever done, like, “If I’m going to be you, I’ve got to make changes from here. From here on out I’m taking the reins; it’s my turn; I’m taking back the power.” So, there is a shift after that episode where she starts to fall in love with people Lennon loved, and that’s where it starts to get a little messy because I think she does fall back into Margot just because she finally sees what she and her sister had and part of her is stuck in the past. She finds herself stuck in the middle of Alison and Lennon.

Which death drew the biggest reaction from you in terms of its visuals?

There are some later that I do love, but I have to say one of the most iconic is Johnny’s death in the gym sequence. There’s so much blood, it’s so gross, it’s so well-done, and it catches everyone off-guard. I watched it with some friends of mine and everyone verbally was like, [sucks air in]. Nobody was really expecting it. And then it gets very gory from there on out.

“I Know What You Did Last Summer” streams new episodes Fridays on Amazon Prime Video.