In "Arrow's" fifth season, the team expanded its ranks by recruiting new members Artemis, Wild Dog and Ragman. All three freshmen heroes have their own sense of right and wrong and are committed to protecting Star City. However, it was recently revealed one of them is a traitor; it turns out Evelyn Sharp, aka Artemis, has been working with Team Arrow's current nemesis Prometheus, learning all her colleagues' secrets and turning them over to the anti-Green Arrow. In Prometheus' hands, that information could spell Team Arrow's doom.

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Ahead of tonight's episode, the mid-season finale, actor Madison McLaughlin spoke with CBR about Madison's betrayal, superhero costumes and Prometheus' identity. We also discuss how she was versed in Artemis' lore before landing the role thanks to being a fan of the animated "Young Justice," and exactly when she realized her brief appearance in Season 4 was meant to lead to bigger, and potentially badder, things.

CBR: Katie Cassidy is on record as saying that putting on the Black Canary costume is a series highlight for her. What was that like for you in Season 4's "Canary Cry?"

Madison McLaughlin: Among all of the shows that I have done, among all of the roles I have played, one of the most-special moments of my life will always be standing in the fitting room, looking in the mirror and having 17 people whizzing around me as they are sewing me into the Canary costume. There was a moment when I looked into the mirror and said, "This is definitely happening." It was really cool. It was such an awesome thing.

It's funny. When I met Katie, one of the first things she said was, "It's cool, right?" We got to share that a little bit.

At the time, did the producers give you any indication Evelyn would be back for a more prominent role?

They did. When I auditioned, I knew there was a chance of coming back. It's "Arrow." We are very secretive. We don't want to let anything out and spoil it for the fans. I didn't know that Evelyn was going to go on to become Artemis until later in the game. It was after I shot my first episode. I knew there was a chance of coming back. Stephen [Amell] was really awesome, too. When we were filming the last day of that episode last season, I was saying goodbye. He was like, "Oh, no. You're going to be back." Sure enough, when I came back, he said, "What did I tell you?" I knew I might come back, but I could never imagine in what way.

How familiar were you with "Young Justice's" version of Artemis?

I was pretty familiar. I had actually watched "Young Justice." I have three little sisters, so we had watched the cartoon. It's great having three sisters and having them be able to look up to someone who is this strong, kick-ass female. When I found out that's where they were going with Evelyn, I was very excited.

How do you feel about how Evelyn changed between "Canary Cry" and Season 5?

I really liked what they did with it. You are still going to see a little of Evelyn's backstory, and why things happened the way that they did. You have to remember – this is a teenage girl with no family. She's just trying to do what she thinks is the right thing. I'm really proud of how it turned out.

Curtis is a tech wiz. Rory is this supernatural force of nature. What does Evelyn bring to the team?

Besides her sarcastic jabs at everybody? It's really special. We've formed such a bond off camera. The writers are amazing. They've brought that into our characters. You can see our dynamic in real life on screen.

As far as the team aspect, Evelyn brings a lot. She's been on the streets. She's coming in with a different perspective than the others. That's why she and Wild Dog formed a bit of a bond. They both have that history of being on the streets and fending for themselves. It's cool to see where she started and where she is now. As a fan of the show, what's great is seeing Oliver help mold her into something better than she already is. It's special to see that bond.

It took a few episodes, but Artemis eventually received her own costume. How did it compare with the Black Canary one?

The Black Canary costume was amazing, because, for me, it was similar for what it was for Evelyn. It was a mantle. It was something already established, and I love what Katie did with the role. She's super-sweet in real life, so doing that was an honor. Then, having my own was special in a different way. It was like, "This is where we're going from here." Plus, I love the color green, so it all worked out.

At one point, Evelyn has words with Oliver. How does she view him?

Evelyn sees Oliver in a similar way that I view Stephen, which is as a total big brother and as a mentor. Stephen took me under his wing when I joined the show, with everything from sharing tips with me on how to carry the bow in a scene, to how to handle this new life of being a superhero and what it entails, to the long hours. Oliver is the same for Evelyn. It's cool for her to finally have a sense of family. Obviously, she's been through a lot because she doesn't open up right away. It really says something that Oliver sticks in there and gives her what she needs to come out of her shell. It's a special relationship that they have.

Artemis goes toe-to-toe with Prometheus on a train – and survives. What did you enjoy about filming that sequence?

That was so much fun. They built a train on a stage and it was actually moving the entire time. It was rocking back and forth. That was one of my favorite days ever on set. We were shooting arrows. Just being me and Stephen that day, it felt like Season 4 again. It was just us and it kind of felt like the old days a bit. It was really fun to do.

It was recently revealed Evelyn is a traitor working with Prometheus. What was your reaction to that bombshell?

Oh, my gosh. It was actually the day we were filming the train scene. Stephen pulled me to the side and he told me a little bit about it. He was the first one to talk to me about it. I was shocked. I was so excited, though, because it opens up a whole new door for the show. Not just for Evelyn, but for everyone involved. I'm excited for the audience to see where we went with it.

In this week's episode, "What We Leave Behind," Prometheus finally makes his big move. In what way is Evelyn instrumental in bringing her teammates down?

I can't say too much because I don't want to spoil it. It's written so beautifully. What I will say is that you will definitely see by the end of that episode where Evelyn stands. I'm really excited to see how everyone takes it, so I don't want to spoil anything. We will see a bit more Evelyn and Prometheus and what exactly is happening and what their plan is.

Evelyn seemed to bond with Curtis, Rory and Renee. Are they collateral damage or does Evelyn lump them in the same category as Oliver?

Evelyn and the boys, the other newbies, are close. I can't think she set out to hurt them. This is what she had to do for her family in regards to avenging them. They are not equal with Oliver, shall we say.

How much are we going to learn about how Prometheus recruited Evelyn and also her motivations?

Over the course of the season, they are going to uncover that and reveal a bit more. All of the answers will come. It's a waiting-it-out thing. Every time I would talk to Marc [Guggenheim] or Wendy [Mericle], I would get excited with where they were going with it. I'm excited that you guys are finally getting to live the same anticipation I've been having for months.

Prometheus' true identity remains unknown. How shocked were you when you discovered who was underneath the mask?

I was very shocked. I was probably more shocked than everyone else. A few of us were together when I found out. It's something I definitely did not see coming. I'm a fan of the show. I've watched it since the pilot and I had no idea where they were going to go with it. I was so caught off-guard. I love that. I'm really excited that nobody else has been able to guess it, either. It's something that you really have to pay attention to. I think everyone is going to be just as shocked as I was.

What else can you tease about the winter finale? How does it set up the back half of the season?

So much happens. The important thing is you really get to see this team as a family. You get to see why they are all doing what they are doing. You see that they are heroes behind the masks, too. It's not just when they gear up and go outside. They are in it for the right reasons. With the betrayal of Evelyn, it really brings that out in all of them. It's going to be a good back half of the season. I'm so proud of what they've put together for us.

Starring Stephen Amell as the Emerald Archer, "Arrow" airs Wednesdays at 8 pm ET/PT on The CW. The series also stars Emily Bett Rickards, David Ramsey, John Barrowman, Willa Holland and more.