Freewheeling Fleetwood Mac-esque folk-rock trio Haim, a group of sisters from California's San Fernando Valley, have come top of the BBC Sound of 2013 list.
The list, compiled using tips from more than 210 tastemakers - made up of music critics, editors, broadcasters and bloggers - aims to highlight the best emerging artists for the year ahead.
"This is the craziest thing we've ever done," Este Haim announces to London's O2 arena.
She is at the superdrome to support Florence and the Machine, and her band is about to end their set with a drum solo.
Heads down, arms flailing, they unleash a four-minute tsunami of percussion and hair. And the audience, primed for the tribal rhythms of the night's main act, absolutely love it.
Half an hour later, the three Haim sisters are back in their dressing room, looking a little less like cavewomen as they demurely sip tea while coming to terms with the fact they have just played on the same stage as the Rolling Stones.
"Don't even talk to me about that, because that is so insane," says 26-year-old Este.
"I've been crawling on the floor, trying to soak it all up," chips in her youngest sister, Alana, 21. "I think I have a little Mick Jagger in me."
An argument ensues as the siblings try to decide which of them is "the most Mick". It goes back and forth for a couple of minutes until Danielle puts her foot down.
"I feel like both of you would be Mick," she tells her sisters. "And I am in the middle of a Mick sandwich."
In fact, if anyone is the honorary Mick Jagger of Haim, it's 23-year-old Danielle. She earned her rock stripes on tour with Jenny Lewis and Julian Casablancas of The Strokes and has clearly picked up a few tips on poise and attitude.
Oh, and she has a lip curl that would put the senior Rolling Stone to shame.
The middle sister, and de facto frontwoman, she is also the quietest member of Haim. While her sisters goof around and riff on British television shows (Alana does a frighteningly accurate impression of Dragon's Den star Duncan Bannatyne), Danielle only really comes to life when talking about music.
Haim started playing together as youngsters, enlisted into a covers band by their estate agent parents.
As Rockinhaim, they covered Motown and Santana at street fairs and charity gigs around the San Fernando Valley. "It was really cool," says Alana. "Until we were about 11."
So in 2006, the girls gave their parents the elbow and ventured out on their own.
"We did what a lot of bands in LA do," says Danielle. "We played around locally, wherever we could play, and we invited all our friends.
"We were scared to ask the main bands for money," Este adds. "We were just so excited to play."
"By the fourth year, we were having to beg our friends to come. Texting everyone, 'please come and pay $10 for the show.'"
Back then, Haim was not a full-time concern. Alana was at high school, Este studying "Brazilian carnival music" at UCLA and Danielle was on the road with Cee-Lo Green.
But it was one of her other touring partners, Julian Casablancas, that finally gave the band a kick start.
"He had seen us play and he said, 'what are you guys doing? What's going on?'" Danielle recalls.
"We didn't know what to do. We had songs on MySpace but no-one really cared. He said, 'just write. Write and come back and hit the ground running.' And that's kind of what we did."
"We went on Haim-atus," laughs Este.
Based in their parents' living room, the band took a year to develop their sound - blending the classic guitar chops of Rockinhaim with the staccato hiccups of their favourite bands TLC and Destiny's Child.
But, for some reason, they could not get the songs to sound right in the studio. There are "four EPs" that will "never be heard" in public, admits Alana.
"Whenever we recorded an EP and got it back, we would put it on our stereo and [after] the first five seconds we would cringe and shut it off."
"In the studio, everything sounds cool," explains Danielle. "But once you put it in your car... We would just throw it away."
The missing ingredient turned out to be sub-bass: The lowest frequencies audible to the human ear, used extensively by dance acts to give their rhythm tracks an added wallop.
Danielle credits TV composer Ludwig Goransson (New Girl, Community) with the discovery.
"We love rap and we love hip-hop," she says. "Ludwig had all these sub-bass samples and when we found them, we were like, 'oh my God. Put that on everything!'"
"He looked at us like we were crazy," adds Alana. "But we'd been searching for that for six years."
The first song Haim recorded with Goransson was Forever, which became the title track of their first EP. Released for free in June, it received near-universal acclaim from music blogs and alternative radio stations like BBC 6 Music and Australia's Triple J.
Bright, bold and melodic, it is not necessarily a musical revolution - but the combination of Fleetwood Mac folk-rock with the intricate hi-hat trills of '90s R&B is, at least, a fresher take on rock than recycled '60s guitar riffs.
That is why Haim were invited on tour by Florence, and by Mumford and Sons. Another stadium-level rock band invited them out on the road this year - but Haim turned them down so they can finish their album.
Their family are thrilled by the success. Grandma Haim flew in from Israel to see the O2 gig, while the girls' parents are vicariously living the dream.
"Before we got onstage for the soundcheck, my dad was up there playing drums," laughs Este.
"He was like, 'OK they're good, I checked them out for you.'
"And we said, 'oh, come on dad, you just wanted to play drums in the O2 arena. Let's be honest.'"