Producers of “Stuart Fails to Save the Universe” have revealed that Kaley Cuoco’s surprise return in episode two was designed to give former “The Big Bang Theory” cast members radically different versions of their familiar roles. Cuoco plays an alternate-universe Penny who leads a resistance movement, rather than the original series’ waitress-turned-actress character, reinforcing the spin-off’s multiverse premise.

Stuart, Kripke and Bert reach a seemingly peaceful Pasadena where neck devices administer electric shocks whenever people become angry or argue. After arrests and 30 months in a rehabilitation facility, they are abducted by Penny’s resistance group, which also includes Denise and Penny’s former boyfriend Zack; co-creator Chuck Lorre said the intention was to offer returning actors a new challenge.