Meryl Streep joined the cast for a season that moved much of the action to Broadway, enlisting a musical theater supergroup to write the songs.

Meryl Streep was looking for levity — she was “in despair of the world for so many reasons,” she said, namely the climate crisis. So she reached out to the funniest people she could think of: Steve Martin and Martin Short, whose late-career resurgence as a double act has included a touring stage show, TV specials and their Emmy-winning Hulu comedy, “Only Murders in the Building.”

“I knew they were doing their tour,” Streep said. “So I just basically called them and said, ‘If you ever want to work together, let’s do something.’”

They did. Short and Martin suggested a stint on the third season of “Only Murders,” in which they play, along with Selena Gomez, amateur sleuths and podcasters who solve murders in their Upper West Side apartment building. Streep said yes without knowing what exactly would be required of her, but the series’s co-creator and showrunner John Hoffman already had a part in mind.

“It really was like the stars were aligned,” Streep said.

As it turned out, not only would she play a prominent guest role as Loretta Durkin, a struggling actress cast in a play directed by Short’s Oliver Putnam; she would also have to sing. (Streep and the other cast members interviewed all spoke before the actors’ strike began.)

That’s because Season 3 of “Only Murders,” which premiered on Tuesday, moves out of the building — well, mostly. There is still a murder; viewers saw Paul Rudd drop dead on a stage at the end of Season 2. And technically, the murder still happens in the Arconia (it’s complicated), the stately prewar co-op of the series’s title.

But rather than risk letting the show’s winning formula become too formulaic, the producers this season took the investigation to Broadway, where Oliver is staging an original musical. And to do it right, they enlisted the aid of a musical theater supergroup led by Benj Pasek and Justin Paul, known for their work on “Dear Evan Hansen” and “La La Land.”

Given the cast and creative team assembled, it all makes for a very star-studded love letter to Broadway. Streep likened the experience to being a “theater company.” Paul compared it to “theater camp.”

“It was just through and through a Broadway experience — there are just cameras filming it,” Paul said. “There was that same sort of ensemble sense, whether it was Meryl or Paul Rudd or Marty or Steve, that everybody was making this show together.”

“Only Murders” has always had show-business jokes — Oliver is known for his legendary flops; Steve Martin’s Charles-Haden Savage is a washed-up TV star — but this season leans even further into its jazz hands impulses. In the premiere, a vainglorious movie star played by Rudd, who is starring in a nonmusical production from Oliver titled “Death Rattle,” is mysteriously offed (it turns out he survived that collapse onstage), potentially by another cast member.

Desperate for the show to go on, Oliver tries to save his already absurd production by turning it into a musical: “Death Rattle Dazzle!,” an all-singing spectacle about infant triplets who might have committed murder.

Hoffman said he could have played it safe, knowing that the coup was just getting the celebrities on board. Instead he decided to get ambitious with the song and dance numbers.

“My idiocy is that instead of containing myself and giving them nothing but great, hopefully, dialogue scenes to do, let’s swing for the fences and go for everything we could possibly dream of,” he said.

And it was the stuff of Hoffman’s dreams. He had thought Streep would be right for the part of Loretta but figured it would never happen, before learning that Short and Martin had been speaking with her. He also had Pasek and Paul on his wish list of potential composers when he discovered that one of his writers, Sas Goldberg, was an old friend of theirs. Turns out, they had already expressed interest in contributing when they learned she was on staff.

“I was like, if they need a ditty, if they ever need anything, we’re obsessed with that show,” Pasek said. When Goldberg texted to take them up on that offer, “it felt like a very serendipitous moment,” Pasek added.

In the show, the songs are written by Oliver, a man who survives mostly on dips and once directed a musical called “Newark! Newark!” In reality, the songs were written by accomplished professionals, who thus had to master a tricky tone: The songs needed to work for a patently ridiculous production but also be genuinely entertaining for viewers at home.

For a complicated, ear worm of a patter song that Martin’s character sings as the detective in “Death Rattle Dazzle!,” Pasek and Paul brought on Marc Shaiman and Scott Wittman of “Hairspray” and “Some Like It Hot.” (“It was a thrill to sing and a thrill to be done with,” Martin said.) The playwright and composer Michael R. Jackson, whose musical “A Strange Loop” won a Pulitzer Prize and two Tonys, contributed a late-season showstopper for Streep.

The Tony-nominated and Grammy-winning singer-songwriter Sara Bareilles was called in to co-write a lullaby titled “Look for the Light,” which Streep’s Loretta, playing a nanny in the musical, delivers to the tiny murder suspects. To prepare, the songwriters listened to Streep’s previous vocal performances to get a sense of her range.

“It’s always nice when you know who you’re writing for because you can sort of tailor something to play to someone’s strengths,” Bareilles said. They emerged with a lovely ballad in which Streep croons in harmony with her fellow cast member Ashley Park, another Broadway veteran (“Mean Girls”).

Streep, however, said she had been intimidated by the challenging melody. On the day of the recording session, she said, she had a “sort of a mental breakdown” after having to prep in only two days and being faced with new orchestration and a group of about 20 people gathered to hear her sing.

“I really felt a responsibility to the music and to the song, which is a beautiful song, and I felt observed,” she said, adding that she “basically pulled a tiny diva move and said, ‘I can’t work like this’ or something.” (She laughed and then noted: “Oh god, that will be horrible unless you put it in all caps in print.”)

There’s a burden to the expectation that comes with being Meryl Streep. “I just feel like sometimes the Meryl Streep of it all walks in like this ship, and everybody thinks, ‘Oh we’re going to watch the launch.’ And I think, ‘Oh yeah, you’re going to see the Titanic go down,’” she said.

Her collaborators sang her praises.

“It’s quite beautiful to witness after all of the laudatory things that have come her way, justifiably so, to watch her be nervous and to watch her be unsure,” Hoffman said.

And Streep, of course, nailed it.

“There was so much tenderness in her vulnerability,” Bareilles said. “She let that speak through her singing.”

The world of backstage drama was, of course, familiar for the central trio. Short got his start in the 1972 Toronto production of “Godspell.” Martin has written two Broadway productions: the play “Meteor Shower” and the musical “Bright Star.” Gomez is the only one of them without Broadway experience, but she has toured as a pop star.

“All three of us know show business and, I’d say, the stage world so well,” Martin said on a video call with Short and Gomez. “We draw upon a lot of memories: You know, the volatile director, the sensitive actor. And we don’t have to exaggerate to do it because we all have been there.”

Still, Streep’s presence can be daunting for even the most seasoned performer, including Short.

“I’m old and I’ve done this a long time,” he said. “And I’m driving to work the first day to work with Meryl, who I’ve known socially through the years but never worked with, and I found myself for first time in a long while going, Gee, I’m a little bit nervous.” During a pause in filming, Short was surprised to learn she had similar jitters.

Selena Gomez was also star struck. “I never in a million years thought I would get to work with Meryl Streep,” she said. Streep’s performance, she added, made her cry. Alas, despite her other career as a pop recording artist, Gomez does not have a song in the onscreen musical.

“I’m a terrible singer,” Martin said. “Selena should have a song, but her character is not in show business.” (Gomez does perform a quick Fosse-inspired dance number in a dream sequence.)

During filming of the stage performances, which were shot at the United Palace in Washington Heights, Streep took up residence in the audience. Specifically, she wanted to watch Martin do his big tongue-twister number, “Which of the Pickwick Triplets Did It?”

“We had a green room we could go to and sit around and bitch, but nobody went,” Streep said. “Everybody sat up there and watched him over and over and over. It was just divine.”

So did the experience cure Streep’s malaise?

It did, indeed, she said.

“They go into everything on this show with this kind of 1940s cockeyed optimism,” she said. “And it was so lovely to be in that world.”