Mumford & Sons brought a Halloween treat to Philadelphia’s Radio 104.5 over the weekend. The British folk rockers and recent SPIN cover stars debuted a tender new ballad titled either “Ghosts That We Knew” or just “Ghosts” — the bandmembers are in disagreement, and it turns out they’re not as mellow as they appear. Watch the band’s in-studio performance of the track below, followed by a brief video interview (via TwentyFourBit).

Whatever they end up calling it, the latest from Mumford and Co. is a delicate, yearning ballad. Much like another tune premiered in the wake of 2009’s platinum-selling Sigh No More, “Home,” the song relies on tenderly finger-picked guitars, banjo, and swelling accordion as Marcus Mumford pleads for a relationship to last. “I will hold as long as you like,” he sings with the slightest touch of throaty rasp, joined by his colleagues’ gently rolling harmonies. “Just promise me we’ll be all right.”

In the interview, Mumford & Sons said that while they wouldn’t rule out collaborating with Adele, there aren’t any plans of a team-up just yet. Then again, the Mumford crew also said they wouldn’t rule out working with Blink-182 — an idea so incongruous it might’ve sounded like a joke, but then the guys started dishing out specific praise for Blink’s comeback LP, Neighborhoods. I guess this is growing up: