Meet the cast of Chicago's 'Book of Mormon'

“If you listened to one and then the other, you would laugh,” he said.

Chicago has been treating Rouleau well so far. He's gotten out to see the city a little and has mastered the CTA. Sort of. He was late for his interview because he went a stop too far on the Red Line and had to turn around.

“I still finding my way,” he said. “But it's pretty similar to New York.”

Ben Platt as Elder Cunningham

Ben Platt, just 19, plays Elder Cunningham opposite Rouleau's Price. He grew up around musical theater and show business in Los Angeles: His father, Marc Platt, was a lead producer of “Wicked”; he was in the national tour of “Caroline, or Change” at age 11. Still a student at Columbia University in New York, Platt is best known as Benji from the 2012 movie “Pitch Perfect.” That was the role that got him the “Book of Mormon” job, he said. Benji “was sort of the nerdy, comic-relief kind of guy” — which also describes Elder Cunningham.

“Cunningham is just one of these guys who's slightly off,” Platt said. “A bit inappropriate, doesn't understand social cues. He's a bit obsessed with Price and wants to please him.”

No resemblance to the actual Platt. Well, few.

“When I get really enthusiastic, I do kind of blurt things out,” Platt said. “We're similar that way. The other parts I've had to sort of work to find.”

Being in a show as big as “The Book of Mormon” has been an amazing experience so far, he said. “It's totally a dream come true.”

Asked to pick a favorite moment, he singles out a scene midway through Act 1.

“The beginning of the show is big and crazy, and then there's this smaller scene with just Nic,” he said. “I always love getting to that scene.” Cunningham and Price are bunking down for the night. “It's like we're having a sleepover,” Platt said.