Marcus Mumford used to be Laura Marling's drummer. It's so weird to think about that now. It's weird, in the first place, to think about Marling even needing a full-time drummer. And it's much, much weirder than that to think that said drummer would go onto become a braying, beefy arena-folk star -- the type of artist whose work would reveal the whole banjo/bolo-tie thing as the pose that it most certainly is. Indeed, three out of four members of Mumford & Sons used to back up Marling on tour. They all come out of the same scene, the short-lived folk-revival thing that blurped up in London in the mid-'00s. Both Marling and the Mumfords can still trace their sounds back to those old shared enthusiasms. But while the Mumfords have gone on to translate that sound into effective-but-hamfisted festival-singalong material, Marling has gone the opposite direction, turning folk music into something personal and insular and strange. Marling's new Semper Femina is the twistiest, most expansive, most particular thing she's done yet, and it's probably also the best.