It’s been a rough four years for Chloe O’Brian.

The plucky CTU analyst and nerd icon who survived six harrowing seasons of loyal service alongside Jack Bauer has returned for a new tour of duty in 24: Live Another Day, Fox’s 12-episode revival. But it was clear from her first appearance that this is a dramatically different Chloe: Her life has taken a decidedly darker turn in the years since she last partnered with Jack, and she’s transformed into a harder-edged incarnation with an urge to reveal government secrets, WikiLeaks-style.

No one has been more fascinated with Chloe’s seemingly unlikely evolution than Mary Lynn Rajskub, the actress/comedian who brings her to life. With some of the tragedies that triggered the transformation now brought to light, Rajskub was ready to reveal some behind-the-scenes secrets as she talked in a conference call with reporters about reviving the fan-favorite character in ways no one ever expected.

On the seemingly inevitable, and yet still surprising, return of 24:

I was very shocked when I found out because I had moved on with my life. It had been four years, and so I spent a few days with my husband and my child and my dogs walking around my pajamas going, “What is happening?” Kind of not believing it, and watching my Twitter feed blow up, and I responded, like, we’re very excited. Meanwhile, I was waiting for them to actually pick up the phone and call and ask me to be involved. And, of course, I said yes without hesitation. How could I not? It was announced that it was in London, and when that was announced, I thought, we’re not actually going to shoot it in London because typically in the past when it’s been in New York and different locations, I've always been inside on the computer with a bunch of stuff that says New York, but they maybe sent a smaller crew over there and this time they said, “No, you're going for the duration.”

On her reaction to the first scripts and Chloe’s new look:

When I read them, they were very exciting and read like classic 24 scripts, and I kind of hopped up at the ends of reading two of them, and then I was like, “Wow! I want to know what happens next!” So that was exciting. And then, of course, in the description it was a very different Chloe. It was very briefly and loosely described, and it wasn't until I got to London and the first thing we did was the Super Bowl promo – that was kind of cool because that got me together with Kiefer [Sutherland] and then we kind of came up with a look that was the first thing we shot. So I met with the hair and wardrobe and makeup, and we just had a great few days of coming up with this idea for this character. So I did it with that team and then we presented it to the producers and everybody and sort of took it from there.

On the secrets of transforming into the darker, grittier Chloe:

It is rough because I am so glamorous and beautiful! [Laughs] For Chloe, it’s a reflection of her pain and her trying to hide, and I feared going into the makeup –feeling like I could never be in the movie where there were lots of prosthetics or anything. Cut to next year and I’m a gargoyle in Lord of the Rings, completely – that would be kind of funny! But we actually got it to a place where it’s very efficient, and most of the time was taken coming up with the look. You probably wouldn’t even really notice them, but there are little clip-ins in my already-crazy hairdo that I have in real life – the asymmetrical hairdo, but we have little clip-ins that make it look like she chopped into her own hair, so, like, little short extensions. And then the tattoos are like kid’s tattoos, where you just put water on them, and they’re really beautifully designed – and there’s ones which you really only see very briefly in 24, but they’re reflective of my husband and my son, Morris and Prescott. And there’s like computer code in the shape of a skull. They’re really thoughtfully designed, but they’re actually pretty quick to put on.

On her first sense of that “coming home’ feeling, complete with Jack’s ‘Dammit, Chloe!” catch phrase:

There was one scene in a car where I'm on a laptop and it was one of those moments where Jack and I had a back and forth, and then in between takes, I was like, “OK, so that was really familiar.” And we were doing this theme, and as you can imagine, it was 24 so everything was super-heightened and intense, and he did throw in a “Dammit,” and it was just awesome because it was really real. So I went from being in the scene and living the “Dammit,” and then when the cut happens we both started laughing and then he started singing, “Welcome back …,” the theme from Welcome Back, Kotter. That thing about our relationship, you know – it's 24. It always surprises me. I never thought this would come back. It was a once-in-a-lifetime thing that is now twice-in-a-lifetime, and the response to it, especially with social media – which just occurred to me was not around very much, not until the tail end, and I certainly wasn't using it as much as I am now as a thing that I kind of go to. I absolutely will go to it throughout the day and right after the show and leading up to the show, and it's amazing, because not only is it like Jack and Chloe never left, but it's heightened even more. So I think this has turned out to be a really cool thing bringing it back.

On the new incarnation of Chloe:

She is really in a lot of pain, and kind of just holding on. She’s not very happy with Jack, and we saw that in Episode 2, and so the first time for me there are moments where, even though I could always find humor somehow in the most intense situations, or some sarcastic remark at least, this time around, she’s in such pain that I wasn’t really able to find any levity at all and that was another surprising layer to play and kind of challenging as an actor. She certainly is very different. It’s like the writers are always holding back from Chloe becoming fully blown with a gun riding side by side. I mean, she is with Jack, but I haven’t really brandished a gun yet, I’ll tell you that.

On her contribution to developing her character over the years:

I have a comedy background, so my approach is very instinctual, and I like to feel it out in the moment, especially in rehearsal. I’m comfortable with things happening really quickly, and adding that to stuff that I’ve done alone going over scripts and then putting that altogether in the moments. Certainly when I first played the character I think I brought a lot to it, just by virtue of my interpretation of what I would be like as that person. And then as we’ve seen the years go on, it turned out to be – I don’t know, I somehow managed to bring humor to a situation where there was none. Now, having said that, I obviously take my job very seriously and love it. I did acting in high school and things like that but it’s interesting to be with Kiefer, who, somehow, we work really well together, but I think we have different styles in that respect.

On whether there are ever really happy endings for 24’s characters:

That’s always something that can never happen. It’s like that forbidden love. It’s that life you can’t have, and I feel like Chloe this time around has been more dragged to the dark side, for lack of a better description, where she’s now part of that in trying to always save the world and deal with these larger-than-life intense situations. There is always the personal simple happiness doesn’t happen. I think back on Chloe and her husband in the past, and they had some moments – there are always moments. There was another guy that I slept with years back, before my husband, and it seems like personal relationships always end badly, but we kind of hope for that happy moment – but maybe not really. But who knows? Maybe Jack will get it. I don’t know about Chloe, to tell you the truth. She’s in a pretty bad way. I think she blames Jack, and I think she, of course, blames herself. She’s just been completely beaten down in every aspect, everything that she tried to do right turned out wrong, and then some. And so when we see her in this packers environment, to me, it was a cool thing that I wouldn’t have predicted for her, but then you start to believe that she could end up there as anti-government and attracted to Adrian Cross, the Julian Assange character. That becomes her rock, and that becomes her whole view of the world of this giving away government secrets. That’s the polar opposite of what she was, and that’s, I think, from somebody who really doesn’t feel she has a lot to live for at this point.

24: Live Another Day airs Mondays at 9 p.m. ET/PT on Fox.