I’m still not sure who paid for Room 330 in the downtown Raleigh Marriott this weekend, but when you get told to go to a party, it’s generally best not to stop and ask too many questions. So last night, just after the end of the IBMA Awards, where Tony Rice delivered a dramatic speech and the words “North Carolina” started to feel like nationalist totems, I stood outside of Room 330 with a few friends, each of us attempting to cajole the others into knocking.

We hesitated. After all, in quickly scrawled black letters, the neon pink sign on the door read “By Invitation Only,” and we could not figure out if we’d in fact been invited. The banjo player, songwriter and singer Abigail Washburn had tweeted that she and her husband, that other banjo player named Béla Fleck, would be doing an impromptu set around 11 p.m. in Room 330. In the year 2013, though, does that an invitation make? What’s more, the third floor of the Marriott seems to be Jam Central at World of Bluegrass 2013, with pickers and a few lucky listeners crowded into rooms already full of double beds or suites lined with overstuffed chairs. You can walk right into most of these rooms, grab a beer, and listen in, but this one had a sign. Did we belong?

Eventually, though, one among us, Daily Tar Heel Diversions editor Allison Hussey, knocked on the door, walked in and gave the rest of us cowards the all-clear. Only a few had arrived for the night so far, and the hosts—polite, but obviously anxious that their suite was perhaps minutes away from being ransacked by bluegrass fans with smartphones—offered us a seat and beer. The room begin to fill, mostly with people who seemed to know each other, IBMA veterans who behaved as if this were at a family reunion and not a musical festival. To wit, when they talked about Tony Rice’s miracle speech, they spoke of his vocal condition and recovery not as fans but as friends. They referred to Washburn not as Abigail, but as Abby.

With her husband and their respective banjos in tow, that Abby arrived near the appointed hour. The pair said hellos, gave some hugs to old friends and sat in two chairs near the front of the room. “Béla and I are both doing things at the IBMA this year, but we weren’t doing anything together,” she said. “So we decided we’d play some songs.”

What followed was, to put it simply, one of the best sets of music I’ve heard in years. I like Washburn and Fleck just fine—she’s got a charming, just-worn voice, and he’s a perpetually adventurous sort, full of incredible ideas that sometimes fall flat and sometimes suggest new horizons in music. But last night, they kept it simple, playing eights songs with two banjos and two voices. (Fleck is not known for his voice, but he harmonized with his wife on a Coon Creek Girls number, unabashedly singing the line “I’m a banjo-pickin’ girl by himself.”) It was unexpected and sublime, a reverent living room concert in the mouth of the surrounding music industry beast.

Appropriately, they opened with a the pensive “City of Refuge,” the title track from her 2011 album. The times of their instruments held tight against one another, holding hands in tessellated licks. They played a mesmerizing instrumental that they’d written over the summer while taking a break from the road following the May birth of their son, Juno. Washburn sang a number in Chinese, articulating the syllables hard and strong, and they finished with the righteous gospel number “His Eye is on the Sparrow.” They played a Washington Phillips tune, and the air left the room.

Offering an introduction to that closing tune, Washburn said that whenever her grandmother would see her play, she’d shout a request for that number from the crowd. It was a sweet tale, and it epitomized the wonderfully cozy atmosphere in the room. I was an interloper, yes, but it was clear that Fleck and Washburn considered themselves to be among family. Before playing a stunning version of the hymn “Am I Born to Die,” she talked about going to the funerals of Doc Watson and Earl Scruggs, and subsequently learning that resplendent tune from a Scruggs LP. She described the nascent anatomic difficulties of sitting to play banjo while raising an infant. Fleck, meanwhile, wondered what would be the bigger miracle—their child speaking at home, or Rice’s testimonial. He playfully chided the suggestions that some attendees had tossed ff for the unnamed instrumental they’d played. Apparently, “June’s Tune” and “Juno’s Lullaby” are a bit too direct. This felt more like a hangout with songs than a concert with the conference’s stars.

That friendly vibe paid off for another banjo player in the room, Fleck acolyte and Kickin Grass member Hank Smith. Smith has already written a classical piece called “Concerto for Banjo” influenced by Fleck’s music, and in January, he’ll debut Blu-Bop, a tribute sextet devoted to the music of the fusion-driven Flecktones. Last night, as we waited for the show to start, Smith showed me one of the handbills he’d printed for the concert. I told him he should turn it into a coupon for Fleck, redeemable for a flight, hotel room and ticket to the show. The idea seemed crazy enough to either get him, well, called crazy or to work, at least for a laugh.

“When I handed him the flyer, he said, ‘So you’re the guy,’ but not in a brusque or confrontational way, more in a ‘eureka!’ kind of way,” Smith relayed this morning. “He was really, really cool and encouraging. He said he would consider coming in as long as his tour schedule allowed it and he wasn’t asked to play.”

The most magical moments at World of Bluegrass seem to be the simplest and most surprising, the ones that speak to the social aspects of the music this festival celebrates. As the event turns toward even bigger stages tonight, we’ll see if it can find ways to maintain that essence.