On the current third season of Supergirl, Reign, played by Odette Annable, is a weapon of mass destruction. Bio-engineered in a Kryptonian lab and sent to Earth, she was raised as Samantha "Sam" Arias. Ignorant of her alien origins, Sam grew up human, has a daughter named Ruby, and serves as CFO of L-Corp.

Yet Samantha’s dark impulses, once dormant, have begun to consume her. She's experienced blackouts as her Reign persona takes control and wreaks havoc. Reign’s twisted sense of justice threatens the entire planet unless Supergirl can stop her -- or if, Sam, somehow, fully regains her humanity.

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In advance of tonight's new episode, "Both Sides Now" -- the last new Supergirl episode until April -- Annable spoke with CBR about Sam’s inner demons, Reign’s brand of justice, the new Worldkillers and whether Sam’s daughter holds the key to Reign’s defeat.

Odette Annable and Katie McGrath on tonight's episode of Supergirl.

CBR: What kind of research did you do for Reign that influenced your performance?

Odette Annable: I had a kid, basically. Coming into the show and knowing my character, Sam, was going to be a single mother -- of course, I’m not a single mother, but, I do now know what it is like to have that love and how real that is. That has influenced my arc and my character in so many ways. It’s not easy to have to think about the dark things that Sam has to think about in protecting her daughter, but it makes it very real for me when I can draw on personal experiences.

It’s been a slow burn for Sam. Why do you feel it was important to establish her home and professional life before introducing Reign?

For the audience itself, it’s more compelling to see someone’s backstory, to be connected with them, to see how much Sam sacrifices and who she is as a person and to see where she comes from. It’s so much more of a compelling story, and a different story, I would say than you’ve seen in any of the other comic book shows. You get to see her origin and you are on her side. You get to see this whole beautiful story unfold, which will be even more heartbreaking to watch.

In recent episodes, Sam suspects something is wrong with her. She’s experiencing these blackouts where she transforms into Reign. Are you approaching her as two separate personalities? Is this similar to Dr. Jekyll and Mr. Hyde?

One-hundred percent. In my mind, they are both two completely separate entities. At the beginning of Season 3, we are exploring what it means to be human, and what humanity is. For me, there isn’t a question whether those two are connected in some way. They are two different entities and for me, that’s what is so fun about playing them. I can do two different things. One is on one side of the spectrum and the other is on the other.

Supergirl has an extensive gallery of villains. What makes Reign a good match for her?

She does have so many villains, but, Supergirl and Reign are connected in so many ways. They come from the same place. They are both Kryptonian. They have so many similar qualities except Reign was bio-engineered and her genetic makeup is different from Supergirl. But I think in Supergirl’s mind, she can help anyone. Sometimes for Supergirl, there’s a grey area. There isn’t for Reign. It’s very black and white. So, it’s going to be interesting to see how that dynamic works out for the rest of the season.

More than once, Supergirl has attempted to reason with Reign. How much do they actually have in common?

I think they have in more in common than Supergirl or Reign would like to admit. They both believe in justice. That is their common thread.

Reign made a striking impression the first time she stepped out. How did it feel slipping into that costume and strapping on the harness for wirework stunts?

What kid doesn’t dream of being a superhero? For me, it was one of those pinch-me moments. Our costume designer, Kiersten [Ronning], is so talented. I was able to go and check out other stuff, too. I got to see the Black Panther costume, I got to go into these warehouses, where I got to see Deadpool. I had the biggest grin on my face. When I first saw the suit on me, you couldn’t wipe that smile off my face. It was incredible.

And, I don’t have a fear of heights at all. My stunt guys are amazing and I just keep telling them, “Keep pulling me up.” They are like, “Are you crazy?” Just relax. I love it so much.

The show is beginning to introduce more Worldkillers. Where do they factor into Reign’s agenda?

Reign sees them as sisters and as allies. For her, finding the next one makes her more powerful and mare united and more complete.

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Can you preview what Reign is up to in tonight’s episode, "Both Sides Now"?

In episode 13, Sam is -- and I can’t say when she’s going to realize that she’s Reign or if she is going to -- but I can say that Sam is trying to figure out what is causing her blackouts. That becomes a storyline in that episode. When she meets Purity, Sam is caught off-guard. She realizes that Purity might be less of an alien than she thought.

Family is extremely important to Sam. In what way could her daughter ultimately hold the key to Reign’s defeat?

That is anybody’s guess right now. If I were to guess, yes, that could be the possibility. For Sam, she’s really strong and her values are so strong. Even when you see Sam freak out when Psi gets in Reign’s mind, you can see how that could be a possibility. If anyone could pull Reign out of Sam, it’s Ruby. Don’t quote me on that, but that’s just my opinion.

"Both Sides Now," the latest episode of Supergirl, airs at 8 tonight on The CW.