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As with Knives Outand Glass Onion,Emmy Rossum nude sex scene in Shameless Rian Johnson has stuffed his latest murder mystery with a slew of stars. Poker Faceis headlined by Natasha Lyonne, but its conceit of a roaming detective allows for familiar faces to pop up each week. Some of those big names blazed across its tantalizing trailer, like Adrien Brody, Chloë Sevigny, Lil Rel Howery, Jameela Jamil, and Joseph Gordon-Levitt. That trailer is just the visible tip of the iceberg of talent in Poker Face; music fans in particular are thrilling over the appearance of lead singer/songwriter of the Mountain Goats, John Darnielle.

Mashable reached out to Darnielle and Poker Faceshowrunners/executive producers Nora Zuckerman and Lilla Zuckerman about the former's role on the show. Maybe you recognized his expressive mug or the signature snarl to his voice, even as he sings some truly (and intentionally) terrible songs in episode 4, "Rest in Metal."

Devoted Mountain Goats fans first picked out Darnielle in a blink-and-you'll-miss-him moment in Poker Face's teaser. (22 seconds in, he's over Sevigny's shoulder.) 

When the trailer hit, fan anticipation grew as we got an even better glimpse of his role.

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With Poker Face's first four episodes now on Peacock, the role behind these glimpses has been revealed.

Who does the Mountain Goats' John Darnielle play in Poker Face? 

In "Rest in Metal," amateur sleuth Charlie Cale (Lyonne) is scoring some quick cash as the merch girl for one-hit-wonder metal band DoxXxology, which has since made a hard turn into has-been-land. In these lean times, DoxXxology's scream queen Ruby Ruin (Sevigny) has a survival job at a home improvement store. Their tour bus is actually a battered RV. Guitarist Al (played by Darnielle) has been making ends meet by hocking memorabilia on eBay.

He even puts his money troubles — and resentments about his impending divorce — into a song: 

"Living on discount macaroni

Can't even get a job with my Uncle Tony. 

You sent your goons to repo my truck

What the actual fuck."

SEE ALSO: Is 'Poker Face' connected to 'Knives Out'?

How did John Darnielle join Poker Face?

In an interview with Mashable, the Zuckermans revealed the origin of Darnielle's involvement. "He's actually a friend of Ryan's and Ram's [producer Ram Bergman]," Nora explained. "When we were writing this episode, we talked about the importance of having a really authentic voice, somebody who can write the songs [for the fictional band]. And Rian — just in the writers' room — casually starts texting."

"He's like, 'I'm gonna text my friend from the Mountain Goats,'" Nora continued, "And we were like, 'What?' I'm a fan as well. I was like, 'Well, there's no way he's gonna say yes.' And then like, 20 minutes later, [Rian's] like, 'Yeah, he's in.'"

In a statement to Mashable, Darnielle shared his end of this exchange, writing:

"Last January I was blowing up Rian's phone with obscure translated-literature noir recommendations, a habit of mine, when he distracted me by asking what I was up to in June. 'I'll be freshly home from tour,' I said.

'Cool,' he said, 'I'm doing a mystery thing that might want some musical guidance, you interested?' The text chain got heated and next thing I knew, the deal was I'd fly up to the Hudson Valley to act in an episode of Poker Facethat involved a rock band, and I'd bring along the songs that band was going to play."

Poker Faceis just the latest collaboration between the musician and the moviemaker. In 2010, Johnson directed The Mountain Goats: The Life of the World to Come, a 51-minute concert documentary named after the band's 12th album. In an interview with the AV Club about the doc, Johnson succinctly described the collaboration that culminated in the doc.

"John [Darnielle] called me up and asked if I was interested in doing [some performance videos]. He also sent me [The Life Of The World To Come] and I just thought the album was so incredibly beautiful — and also, the album felt whole. It felt like an album that you sit down and listen to from cover to cover. So that's where the idea came from of shooting the entire album back to back. And second, [there was] this notion of doing it with a really lightweight digital camera in a space that was just lit with stage lights, and just shooting the whole thing in one go — just kind of having it feel like you're in the room with John as he plays these songs."

But Johnson's appreciation for Darnielle dates back even further. As the same interview notes, the midnight run to Jakarta mentioned in Johnson's sophomore effort The Brothers Bloom (2008) is a nod to Darnielle's blog, Last Plane to Jakarta.

Did John Darnielle write the songs in Poker Face's "Rest in Metal"?

Over the course of the episode, there's a mix of good songs and — as Ruby puts it — "turd" songs. Darnielle was entrusted with writing the lot, though the writers' room offered some guidance.

"Some of the lyrics came bundled into the script," Darnielle told Mashable. "The rest I wrote myself."

Lilla Zuckerman concurred, though she put it this way: "Some of the lyrics are ours. But he made our rotten lyrics absolutely lovely. Just a testament to his talent."

Asked what it was like to write for different characters within the episode, Darnielle said, "Rian sent me the script well ahead of any work I needed to do, so I had a while to live with it. Writing in character is basically what I already do — the speaker in my songs is almost never 'John Darnielle.' And quite often it's a fictional character with a pretty involved backstory."

How did John Darnielle found his inner metal head?

As DoxXxology is a metal band, their sound for "Staplehead" and the criminally catchy "Eat My Sucker Punch" are pretty different from the Mountain Goats' folk-rock vibe. So Darnielle tapped Jamey Jasta from the metalcore band Hatebreed for help.

"He wrote some music and sent me files," Darnielle recounted, "I finished up my lyrics and sang them over what he sent, and then sent them right back so he could have somebody put a vocal onto them for use in the show. Of many great exchanges during that whole process, Jamey saying I should pick up acoustic duties because the studio acoustic was tuned to B was easily the most metal. Tuned to B! An acoustic guitar!"

John Darnielle took on acting, advising, and improvising in Poker Face.

Darnielle faced other challenges in making the leap from stage musician to TV actor. "Come June, I went up to the Hudson Valley [for Poker Face]," he said, "And learned that actors work literally from 6 a.m. until way past midnight daily. On tour, I don't have to report to the stage until 3 at the absolute earliest."

Despite this jarring difference, Darnielle was an adored multi-hyphenate on set. "He was so much fun," Nora recalled, noting that not only did Darnielle improvise some of the song lyrics heard in "Rest in Metal," but also he became a consultant on set. "Having a real accomplished musician on stage with actors and giving them tips," she marveled, "...having somebody who's so knowledgeable about real-world stuff and even helping the props guys sort of say like, 'Oh, actually, I would connect the amp this way.' We were like, 'We have a songwriter, actor, consultant, all of that.' And he was great."

Among the songs that he experimented with on set was the confessional jam "You Can't Unmurder Someone," which brandishes the line "We electrocuted a lamb for the keys to the kingdom."

"The pivotal song my character sings in the big reveal scene was half prepped in the script and half ad-libbed onset," Darnielle said. "That was sort of my moment to justify my presence among proper actors. Making up a song in front of people is something I can occasionally do, and when it works right it's kind of electric."

Electric. Get it? He's clever, and he's not wrong.

"By that point in the filming," he recounted, "I'd been living in Al's clothes — quite literally; he wears orthopedic shoes and army surplus finds — for a couple of weeks. And I had a feeling for how dark the world's looking to him now that the one fun thing he had working, a little work in a rock band, has turned into a nightmare. But since it's also comic — I mean, 'comic nightmare' is kind of specifically my zone, finding a way to inject real emotion into a situation that's equal parts hilarious and horrifying is my exact lane."

And that's how you turn murder into a killer ballad.

Poker Face is streaming on Peacock.