[Warning: The below contains MAJOR spoilers for Season 5, Episode 4 of Supergirl, "In Plain Sight."]

Kara (Melissa Benoist) learned William Dey's secret identity in Sunday's episode of Supergirl as her investigation into her new colleague continued.

Kara discovered someone faked the death of Obsidian's lead accountant and followed a lead to an apartment just before he walked in. He's undercover investigating Andrea Rojas (Julie Gonzalo) and her involvement in a criminal conspiracy, he revealed. The "toxic jerk" he's been was all a lie.

"I respect William," Staz Nair told TV Insider. "He's willing to sacrifice friendships, his own sanity, his own life potentially for the sake of doing something for the bigger picture."

Elsewhere in the episode, James (Mehcad Brooks) realized what he wanted to do with his post-CatCo career: return home, buy the Calvintown Gazette, and show the town there's someone willing to fight for them.

Here, Nair breaks down the real William Dey, discusses Brooks' exit, and more.

So, who is the real William Dey? Have we finally met him at the end of this episode?

Staz Nair: We are very complex as individuals and there are many layers to every person. That being said, what you get to see in Episode 4 is a far more truthful side. It is the integral side of him as a journalist, as a person. You get to see a side of him that demonstrates a sense of selflessness as opposed to the selfishness you've seen. In essence, yes, you are getting to see more of the real William, but there will be more to come.

We see him tell Kara how much he respects and likes her writing. What was his first impression of her, as a person and as a journalist?

He respected her tenacity. Where they connect as journalists is their need for truth, their willingness to fight for truth, their willingness to go up against any obstacle to expose and reveal the reality of whatever situation they're trying to reveal.

He respected her, but he used her willingness and not naïveté, but her salt of the earth excitement and exuberance against her and tried to play off that and pretend he disliked that or found that annoying or found it overbearing or made her look distracted or unprofessional. He had to [ignore] what he liked about her in order to survive and protect everyone around him.

How does this new honesty from him change the dynamic between them moving forward? At work, he still has to act like the same person he has been, but away from the office, he can be who he really is.

Yes. That's going to be a difficult thing for William because it's nice to know he has someone who knows the truth. That's a safe space. We all need someone to be able to turn to. That's very, very exciting for William. But at the same time, it makes it somewhat harder because it means you let your guard slip when you have let someone in.

We also learned William's marriage is a lie. What can you say about his personal life that isn't a lie?

William puts up this facade and these walls to protect himself. He's trying to uncover Andrea Rojas and this conspiracy that his family has found over many years. In order to do that, he creates these barriers that people have to get over — or don't get over — in order to get to him. The wife is there to provide another barrier. It means, oh, he won't socialize after work, he has a wife to go back to. It breaks any romantic interest anywhere and it makes him basically emotionally detached from anyone.

The real William that you're going to get to see is a nice, caring, kind man. He's been broken by life and experiences. Being a journalist is tough. I don't think it's the first time he's gone undercover. It's a hard life, but through that he has found a way to be kind. You see that in Episode 2 when he works in the soup kitchen.

When people come across suffering or obstacles in their life, they allow that to become them. William tries to let that make him better.

Now that we know he's investigating Andrea, how much of his investigation are we going to see him explain in the next episode? Are we going to learn a lot?

Everyone will be thoroughly satisfied with what they discover, across the board, not even just in my story, with this next episode. It's a very fun episode.

William is supposed to be this ace reporter and he has that line about getting the Pulitzers for the story, not his writing. So how long will it take him to realize that Kara's Supergirl?

You know when something's so in front of your face, you can't see it? That's the way it is. I have no idea when he's going to find out. I think it'll be interesting to see what happens when he does and how he reacts because he'll probably feel like a fool he didn't know all along.

[That line about the] Pulitzers, he paints by numbers. He knows how to make something good formulaically. He's a mathematician when it comes to his work as a journalist, whereas Kara puts her heart and soul into it. Kara puts everything, every fiber of her being, into her writing for the sake of writing the right story, the truthful story as she believes it be.

This week's episode also saw James leave National City after the changes at CatCo. How does it affect William to have to stay undercover and not speak up, even though he's seeing how it's affecting people there?

For someone like him, who wants to go fight for the truth, to sit there and have to shroud the truth, it's very tough. Like with every person, we have a bigger purpose, [which] supersedes and transcends the immediate problem. The immediate problem in this case is people dropping like flies because of the integrity of CatCo being shot. Yes, that's terrible, but he's thinking about winning the war instead of winning the battle.

Sadly we didn't get anything between William and James before James left.

That's a real shame. Mehcad is a very, very interesting individual. The few hours we got to spend together on set were a real meeting of the minds. I find him fascinating and I wish him the best, and I totally agree, it's a shame we didn't get to work together more.

How does that absence affect the show moving forward?

This thing we do for a living, there's a professional aspect to it, there's a creative aspect, and there's a personal aspect. All three things get affected when someone leaves. Some people are losing a friend, some are losing a fantastic actor, some [fans] are losing their favorite character on the show.

This is sadly the nature of the game. We move on, whether it's to better things, to different things, or just move on. It's a very transient, fleeting industry, and it's tough. I know how hard it is for everyone because of what a family they've created here on this show that I already feel so integrated into ... It's a transition, a change like anything. But we move on and we move forward.

How does he think this investigation of his is going to end?

In his heart of hearts, he doesn't know how it's going to end. He knows he won't stop until he uncovers the Rojas family. You know when you know the destination, but you don't know how you're going to get there? That is essentially what William's approach is. He's tried so many angles before. He's said he's been doing this for two and a half years. He's not pussyfooting around this. It's been a long time coming. Through hell or high water, he will find a way.

Supergirl, Sundays, 9/8, The CW