Big Bang's Kaley Cuoco Says Making Stuart Fails To Save The Universe Episode 8 Was Like 'Shooting A Transformers Film' — Watch Interview

Firing Squad Penny shows no mercy in Kaley Cuoco's return to "Stuart Fails to Save the Universe."

The third-to-last episode of Season 1 transports Stuart, Denise, Bert, and Kripke to war-torn Pasadena, where disobeying the orders of their commanding officer, Captain Williams (played by "Big Bang Theory" alum Dean Norris), lands them before a trio of military judges. They're represented by the world's worst JAG, Captain Seibert (fellow franchise vet Joshua Malina), who falters opposite opposing counsel Major Penny — at which point the gang is sentenced to death by firing squad.

Luckily, Stuart buys them enough time to activate the quantum entanglement device and escape to another universe. But there's a hitch: Penny is accidentally transported with them and transformed into a centaur!

It's quite the evolution from the AI resistance leader Penny viewers met in Episode 2 of the "Big Bang Theory" spin-off. Even Cuoco admits she wasn't entirely sure what she was getting herself into the second time around.

Cuoco, speaking exclusively to TVLine about her Episode 8 appearance, sat down with us all the way back in January, one month after TVLine visited the "Stuart" set and as the actress was promoting her MGM+ limited series "Vanished."

Cuoco's involvement in the "Big Bang Theory" spin-off actually dates back years before she ever stepped onto its elaborate sets.

"My relationship with Chuck Lorre — we go very deep — and so I always said I would do anything for Chuck, really forever," Cuoco tells TVLine in the video interview above. "He called me almost three years ago, this is true, just called me out of the blue and said, 'Hey, if we ever do a spin-off, would you help me out and revisit Penny?'"

And she didn't require any details before giving Lorre her answer: "I didn't even ask. It was a yes." But after nearly three years passed without another word, "I thought, 'That's probably never going to happen.'"

Then, seemingly out of nowhere, Cuoco was told she was shooting "Stuart" the following week.

"I had no idea what the hell I was doing," she admits. "I was like, 'OK... who am I playing?' 'You're Penny, but you're not Penny.' OK? 'You're Penny, but you're in a different world.' OK? ... It was such a mindf–k."

Rather than attempt to make sense of the multiverse mechanics, Cuoco decided to embrace the absurdity: "I went in very blind. I didn't ask a lot of questions. I just [told myself] that I'm not going to try and understand this because it was so crazy."

There was another unusual aspect to Cuoco's homecoming: After spending 12 seasons surrounded by the "Big Bang" ensemble — including original co-stars Johnny Galecki, Jim Parsons, Simon Helberg, and Kunal Nayyar — she was returning to Penny without them.

"I wasn't with any of my — I mean, Stuart and all of those amazing guys — but none of the main guys who I was with for so long," she says. "So I was like, 'How am I going to do this?'"

But any apprehension quickly dissipated once she arrived. Many of the crew members were familiar faces from her "Big Bang" days, giving the otherwise surreal experience a sense of familiarity.

"I knew basically everybody, so it felt like being home," she says.

What did catch her off guard was just how big the production was, with sets needed at both Warner Bros. and Universal: "I couldn't believe it. It was like we were shooting a 'Transformers' film. It was so huge — huge sets, huge setups, just massive, and really incredible."

As for whether she understood all the sci-fi jargon...? "Absolutely not," Cuoco answers. "I had no idea what I was saying. And I just hope it comes across like I knew what I was saying because it was a different universe for Penny, and it was a different universe for me."

TVLine was on set as Cuoco filmed the centaur sequence, watching from video village as she galloped around the comic book store — a sentence that would have seemed fairly implausible at any other point in the franchise's history. Even Cuoco had trouble explaining to her own team exactly what she'd spent the day filming.

"'If you gave me a million dollars in my hand right now, I could not tell you what I did today,'" she recalls telling them. "As a viewer, I'm going to be very excited to watch it and see this world they created, because I can tell you that being there felt massive, and it felt like a huge feat and a really cool undertaking.

"[Chuck Lorre] said he always wanted to do a show like this, he always wanted it to have a sci-fi aspect, so I think Chuck is living out some sci-fi dream himself," she says. "I was just glad that I got to play for a few days. It was definitely special."

And if you're wondering how exactly one prepares to play a human-horse hybrid, it turns out Cuoco came unusually qualified: "Luckily, I have horses, so I kind of knew how to act."