Niecy Nash and Nathan Fillion Preview Potential 'Rookie' Spinoff (Exclusive)

The stars dish to ET about Sunday's backdoor pilot, which introduces Nash's Simone Clarke.

The Rookie world is expanding.

Niecy Nash joins the fray as Simone Clark, the oldest rookie in the FBI Academy, for a two-hour backdoor pilot setting the table for a potential Rookie spinoff. In Nash's debut episode, which airs Sunday, Officer John Nolan (Nathan Fillion) and the Los Angeles division of the FBI enlist the help of FBI trainee Clark when one of her former students is suspected of terrorism following an explosion at a local power station.

"Simone is so fun to play," Nash tells ET's Rachel Smith of her character. "It's very very different from the shows I'm coming off of, so coming there and knowing that part of this woman's journey -- not specifically of her wanting to be in the FBI -- but about her course-correcting or making a pivot at a stage that most would consider later in life, that's what's delicious to me. For people to come with her on her journey the same way they did with Nathan."

Nash has played a cop before, during her time on Reno 911!. But she likened this character and the role to be drastically different, thanks to its dramatic undertones.

"When I used to play a cop on Reno 911!, it was like Keystone Cops [a group of incompetent officers featured in a series of comedies in the early 1900s]," Nash recalled. "And the more mistakes you made, the better it was. So for this particular job, I love that I actually had to get training on exactly how you're supposed to hold the gun because in Reno I could just sit it on top of my head and nobody would care. But to actually be trained properly and how to drive stunt cars properly, there was a lot that I had never experienced in the industry, even though I've been in it my whole life. So I took it all in."

Raymond Liu/ABC

"She nailed it," Fillion praised. "She was in a shootout [during one scene] -- dropping a magazine, sliding in a new one. It was poetry in motion."

Nash offered an intriguing tease for Simone's introduction. Her character, for her part, has been described as "a force of nature."

"Simone Clark is definitely a flirt," she previewed. "She flirts with men. She flirts with women. She thinks everybody wants her, even though they're just simply saying hello!"

Asked whether he's offered any advice to Nash on possibly leading her own unit if ABC moves forward with the Rookie spinoff, Fillion said Nash is "a very capable lady" and can very much hold her own.

"The one thing that I will tell you is that I've been around the block two or three times, but as a whole cast and crew I haven’t worked with a kinder group of people and everyone was so welcoming," Nash expressed. "I mean, every single person, from the time you walk out the trailer, from the time you get to set, 'Do you need anything?' And it's genuine! 'Are they treating you OK? How can I help you?' I definitely felt the support."

The Rookie airs Sundays at 10 p.m. ET/PT on ABC. 

To stay up to date on breaking TV news, sign up for ET's daily newsletter.