A few years ago, Sebu Simonian placed an ad on Craigslist looking for production work. L.A. songwriter Ryan Merchant replied right away. "I remember checking out Sebu's work and feeling like he was a kindred spirit," says Merchant. In fact, he was the only person who answered the ad. Says Simonian, "As fate would have it, we had chemistry."
Soon the pair were recording jingles for companies like Hallmark and Honda, and gigging around town as Capital Cities. They began working on this year's surprise Top 10 smash "Safe and Sound" back in 2009, experimenting with several different styles before hitting on its signature horn-and-synth riff. "We put it on the blogosphere," says Merchant. "Then it became a hit in Peru totally randomly." That led to a deal with Capitol Records, who helped get the song heavy airplay and released the duo's debut LP this past summer.
For their next single, they're considering "Farrah Fawcett Hair," featuring Andre 3000 and tons of pop-culture references, from Bitches Brew to Back to the Future Part II. "We wanted to write a song about things that are undeniably good," says Merchant. "And Back to the Future II is a crazy movie."
This story is from the December 5th, 2013 issue of Rolling Stone.