Stuart Fails to Save the Universe episode two sees the return of a major Big Bang Theory star — but not as fans remember them.

Set after the events of the original sitcom, HBO Max’s new spin-off follows Stuart Bloom (Kevin Sussman), the comic book store owner from The Big Bang Theory, as he accidentally destroys a multiverse device created by Sheldon Cooper and Leonard Hofstadter.

With the help of familiar faces Bert (Brian Posehn), Barry Kripke (John Ross Bowie) and Denise (Lauren Lapkus), Stuart sets off on a mission across alternate realities to restore order to the universe, encountering new versions of characters fans will recognize from The Big Bang Theory along the way.

The latest episode, which aired Thursday night, sees the group enter a reality in which all humans have a device implanted on their necks that delivers an electric shock whenever they argue or get aggressive.

This eventually leads them into a 30-month reeducation facility designed to eliminate conflict. But after completing the program, they are unexpectedly abducted and taken to an abandoned warehouse.

It’s here, once their hoods are removed, that Kaley Cuoco’s Penny reveals herself.

Rather than the blonde, aspiring actress-turned-pharmaceutical sales rep from The Big Bang Theory, this alternate version of Penny has brunette hair and leads a resistance movement against their AI-controlled world alongside her ex-boyfriend Zack (Brian Thomas Smith).

“A big part of it was offering them a challenge to do something entirely different,” co-creator and executive producer Chuck Lorre told Variety of bringing back some original The Big Bang Theory characters in new forms.

“As you’ve seen in Episode 2, Kaley’s not playing the server in the Cheesecake Factory. It’s still Penny, and now she’s a badass guerrilla leader. That was part of the design from the very beginning. In a multiverse environment, these characters could recur as themselves, but with an entirely different backstory.”

The Big Bang Theory ran from 2007 to 2019 on CBS and made global stars of its core cast members, Cuoco, Jim Parsons (Sheldon), Johnny Galecki (Leonard), Kunal Nayyar (Raj Koothrappali), Mayim Bialik (Amy Farrah Fowler) and Simon Helberg (Howard Wolowitz).

It followed a group of socially awkward scientists and their friends as they navigated relationships, careers and everyday life in Pasadena, California.

The wildly popular show reportedly ended because Parsons turned down $50 million to return for a 13th and 14th season.

Stuart Fails to Save the Universe airs Thursdays at 9 p.m. ET on HBO Max.