Yvonne Strahovski Yvonne Strahovski

[SPOILER ALERT! This story contains major plot points from the upcoming season of Dexter. Read at your own risk.]

Sarah Walker, no more.

Yvonne Strahovski, formerly known as Chuck's sexy secret agent, is about to shock and awe audiences this fall when she takes on a killer new role on Showtime's Dexter.

Dexter Season 7 Scoop: How will Deb react to Dexter's secret?

Hannah McKay (Strahovski) will cross paths with Dexter (Michael C. Hall) this season while working on a cold case. Why is Hannah such an expert? As TVGuide.com first reported, she went on a Bonnie-and-Clyde-like killing spree with her boyfriend in her younger years, and turned against him when they got caught. Charming!

"This character is going to be completely different," Strahovski told TVGuide.com following Thursday's Comic-Con panel. "It's a 180 from the Sarah Walker that everyone knows me to be on Chuck. I get to play someone that's darker and in an environment that's darker. The show is obviously very dark. The energy is so different."

The stark contrast between Hannah and Sarah is exactly what attracted Strahovski to this role — that, and the possibility of cursing on TV. "I've never gotten to say the F-bomb on camera, and maybe I'll get to say the F-bomb on an adult show," she said with a laugh. "It's little things like that."

Comic-Con: Watch the first two minutes of Dexter's Season 7 premiere

Of course, any new female character who joins Dexter will draw comparisons to Lumen (Julia Stiles), but Strahovski stresses that they're two very different characters. "We met Lumen in such a damaged place," she says. "The first time we saw her, she was a victim of the barrel guy. She was in such a fragile spot. When we meet Hannah, it's not like that. It's a different beginning when she meets Dexter because she's coming to help solve an unsolved murder. They need her to help them get some information. She's very much a together person when we first meet her."

While Strahovski was shy to even confirm what executive producer Sara Colleton told us about her character, she did get excited about the possibility of showing flashbacks to Hannah's killer past. "I wonder the same thing actually and I might ask that same question when I find the writers of the show here," she says.

Bottom line: Sarah Walker may have been a killer in her own right, but she's long gone. Bring on Hannah McKay! "It's such an amazing show and to be changing it up like this, I couldn't ask for anything better really," she said.

Are you excited to see the Chuck alum on Dexter?

Check out the first two minutes of Dexter's season premiere below:

Dexter returns Sunday, Sept. 30 at 9/8c on Showtime.