Serena Brook and Sue Scott were trying to sort out a little roommate squabble.

Brook was the level-headed one, calmly trying to negotiate the logistics of a grocery store run. Scott was being high-maintenance, dramatically waving her hands in the air and requesting “Paper! Paper of the toilet.”

“Toilet paper? You need toilet paper?” Brook said, exasperated.

Sound like a domestic partnership on the rocks? It’s not. At this rehearsal a week ago, the tension came courtesy of the writers for “A Prairie Home Companion,” who pitted Brook — the show’s first new actor in more than 20 years — against the woman she essentially replaced.

“I love you guys as roommates,” commented Chris Thile, who took over as host from public radio saint Garrison Keillor last fall.

He and Brook will wrap up their abbreviated debut season Saturday at the Fitzgerald Theater in St. Paul.

If there is tension between the two women — they insist there isn’t — it wasn’t evident at rehearsal as Brook, 30, played straight woman.

The Eagan native’s chance to be silly came in an earlier sketch, playing a bubbly Minnesotan who picked up Thile in a new self-driving car. Scott was in that sketch too, but as the vehicle’s soothing computerized voice. It would hardly have been funny without her.

And yet, the whole reason Brook landed a job on “PHC” is that the show’s producers wanted a younger actress, someone who sounded like she would go on a fuel-efficient joyride with an attractive young mandolinist.

“Sue Scott is miraculous, arguably the greatest female radio performer in the world,” Thile said of the actress who has been a cast member since 1992, but appeared in only three shows this season. “But I think it was of tantamount importance to have a believable romantic interest. You know, a counterpoint for the host. There’s something about being able to believe the romantic tension in a sketch. That’s just such a huge part of life. Romance.”

As ageist and sexist as that may sound, Thile has a point. Think of all the times Keillor’s Guy Noir walked into a bar and Scott was there to play an aging femme fatale, or a past-her-prime barmaid pouring drinks for Dusty and Lefty in “Lives of the Cowboys.”

Could Scott voice a millennial? Sure. Could a middle-aged woman have a crush on Thile, a 30-something MacArthur genius? Entirely possible. But Lake Wobegon is not Cougar Town. And so, quietly over the summer, producers put out the word that they were auditioning to replace Scott. Brook heard about the gig through Talent Poole, her agency in St. Paul.

“I sat in my little walk-in closet in my apartment with my mic and made silly noises,” Brook recalled.

A week and a half later, the tall actress with an easy laugh found herself at the Fitzgerald Theater, reading scripts with sound-effects wizard Fred Newman, Tim Russell, Thile and creative producer Dan Rowles. Brook had never met any of the men before.

“They were so welcoming and so warm, and it was just so much fun,” Brook said. She read scripts for an hour. “I left thinking, ‘Well, that was a wonderful life experience. If nothing comes of it, I can cherish that moment.’ ”

Something did come of it — eventually. On Labor Day she was in New York’s Central Park while visiting friends when the call came, asking her to join “Prairie Home” for at least the first couple of shows. That offer then got extended for the 13-show season.

The timing worked out well for Brook: She already had a gig this spring in Chanhassen Dinner Theatres’ production of “Grease,” which begins previews March 3, but after getting married in August, her fall was open.

“It was a stars-aligning sort of thing,” she said.

Her parents were ‘PHC’ fans

Brook may be known in the Twin Cities mostly as a musical theater actress, but her résumé includes everything from off-Broadway children’s theater to Target commercials.

Those varied credentials appealed to “PHC” producers, who didn’t hire Brook for her ardent fandom of the public radio show.

The actress admits that her parents were the listeners in her family — an acknowledgment that lends credence to Thile’s effort to attract younger audiences.

After last Saturday’s taping, Brook’s father, Eric, wanted to chat with Newman, not rub shoulders with the rock band Lucius or comedian Tom Papa.

He talked up his daughter to anyone who would listen, and reminisced about the hours he spent driving his children to Hebrew school, his daughter singing show tunes and his son complaining about the racket. Performing was “all Serena ever wanted to do,” he said.

Her mother, Judith Brook, was equally giddy backstage, and extremely proud: “There was just one part like this, and just one show on the air like this, and she got the job.”

Brook took tap and jazz dance lessons as a kid and started acting seriously in high school. After earning a drama degree from University of Minnesota Duluth, she did what most young actors do, which is try to make it in New York. There she landed a role in the original cast of the off-Broadway musical “Dear Edwina” and took improv classes from the Upright Citizens Brigade.

But as a tall brunette with corkscrew curls, she wasn’t what most directors were looking for in an ingénue, and she was still a bit young for many character roles. Most of her work ended up being far from Manhattan, including two stints as Mama Who in the national tour of the musical “How the Grinch Stole Christmas.”

Then in 2013, Brook was cast as Tzeitel in Chanhassen’s “Fiddler on the Roof.” Nick White, her then-boyfriend and now-husband, followed her to play horns in the pit orchestra, even though he’s from Florida and even though it was a polar vortex winter.

“It was a testament to his love,” Brook said, laughing. More practically, “the appeal of working where we live was a big draw.”

They got a cat named Vicky, an apartment in the Whittier neighborhood of Minneapolis and became regulars at Chanhassen. Brook’s other Minnesota gigs include acting in 7th House Theater’s production of “Jonah and the Whale” at the Guthrie, and doing voiceover work for Target, Caribou Coffee and the Minnesota State Lottery.

How she got the job

Backstage after Saturday’s show, Thile said “Prairie Home” producers sent him MP3 files of more than a dozen actresses reading sketches, but after sitting down with Brook, he didn’t listen to any of them.

“She killed it,” Thile said of her table read. “It was like I was hearing the voice I wanted to hear in my head, the voice I didn’t know I needed to hear.”

American Public Media, the St. Paul-based distributor for “Prairie Home,” has not yet announced plans for the show’s next season — reruns of old Keillor programs will fill the remainder of this year’s schedule — but Brook is game to be a part of it.

“It’s this crazy thing that all these artistic worlds that I love are combined into one: acting, singing, voiceover, improv, and even writing a little bit. I’m so, so lucky to be doing what I love.”