When the spirit moves Paul Janeway, watch out. “I tell security at every show, ‘Look, I know this is weird, but I don’t know what I’m going to do,’ ” says the frontman for retro-soul outfit St. Paul & the Broken Bones. “It’s more like Iggy and the Stooges than James Brown in that sense… if you’re singing a song about heartache and sadness, your body should react to it.”

At the recent Austin City Limits Festival, that meant rolling around on his back, crawling under the drum riser, breaching the security pit and—for his first time ever—crowd-surfing. “For some reason I jumped off a 9-foot stage,” the 33-year-old singer says. “I could have broken something. I don’t know if it’s about the performance or getting close to people, but it varies from night to night.”

Physical manifestations aside, Janeway mainly surprises people when they hear his soaring, full-throated voice, which recalls R&B-soul shouters like Otis Redding and Percy Sledge, not the spectacled white guy they see onstage.

If the besuited singer looks more like a CPA than a rock star, that’s not far off the mark. Janeway studied accounting in college before pursuing music with his Alabama buddies. He’d grown up singing in church but didn’t even get onstage with a band until his early 20s. “People were like ‘Oh!’ And I thought, ‘Oh, maybe I’m pretty good,’ ” Janeway says from his Birmingham home. “[I looked at] people’s faces. They were paying attention. So it just kind of snowballed from there.”

St. Paul & the Broken Bones forged a surprise smash with their 2014 debut Half the City, inspired by soul icons like Redding and Sam Cooke that Janeway heard alongside gospel while being raised in a strict religious household.

Their second album, Sea of Noise, released in September, tweaks the band’s palette beyond the retro, drawing on influences from Prince to Portishead to John Barry, known for his vintage James Bond soundtracks. “Flow with It (You Got Me Feeling Like)” percolates with congas and slinky horns, while “Midnight on the Earth” adds funky chops and chants, plus a synthesizer break before its orchestral swell.

In turn, Janeway changes up his vocals, letting his falsetto fly. “The last [album], it was all about just going at it a million miles an hour,” he says. “What you realize is you have to explore more nuance and ways to approach singing. I’m still kind of discovering my voice.”

Sea of Noise signals that shakeup from the hymn-like prelude of “Crumbling Light Posts,” inspired by a Winston Churchill quote about England being a crumbling lighthouse in a sea of darkness. Other songs mull darker territory, asking how to decide what’s right in a world that’s wrong. “That’s my daddy with a gun, shooting someone else’s son… a bullet with intent for the color of his savior,” Janeway sings in “Brain Matter,” posing the question “Can we find love in a black hole?”

“It’s kind of this exploration of Southern identity in modern times,” says Janeway, who brings the Broken Bones to Royale on Nov. 5 and 6. “There’s not a lot of answers on this record. It is a little more bleak than I am as a person.”

The band’s ascent has been an adjustment for his parents as well. His father told him that if the music fell through, he could still have a job at the construction and paving company. “I knew I wanted to do music, but that’s not realistic. A lot of people want to do music,” Janeway says. “It’s been a process. My mom doesn’t like the cursing. She says, ‘You keep St. Paul onstage and don’t bring him around me.’ ”

So he’s not an accountant—or a preacher, which was what Janeway initially saw as his calling. “I’m a fairly liberal guy, and where I grew up, that’s kind of frowned upon,” he says. “I just fell out of love with [the church], but I realized that I have genuinely loved the performance aspect. I enjoy being like a conduit to move people and extract emotion out of people. And that’s what I do for a living.”

St. Paul & the Broken Bones play Royale on Nov. 5-6.