The first time I heard "Japan"-one of the better cuts from CocoRosie's latest, The Adventures of Ghosthorse and Stillborn-the Casady sisters were opening for Antony and the Johnsons at Boston's Paradise Rock Club. The then-unreleased "Japan" recalled a number of their most experimental songs: whispered, Appalachian vocals over a tropical beat and topical lyrics put to an antiquated sound, not unlike the baroque-pop luminary Van Dyke Park's Discover America album, which in 1972 embraced the sound of 1940s Trinidad. Except that after about three-and-a-half minutes, the classically trained Sierra Casady wrapped a Kabuki mask around her face and sang a haunting minute-long aria. Sierra paused. The audience-mostly seated, largely older than the typical Paradise set and profoundly confused-was silent. Faintly, a steel drum returned. Her shoulders hunched as though remembering a particularly naughty secret, Bianca Casady peered out at the audience: "Everybody wants to go to Japan," she cackled with an assumed Caribbean inflection. "Everybody, just hold hands!"

Unsurprisingly, a very Bohemian quality is at work on CocoRosie's albums, perhaps more so than with the freak-folk bands to which CocoRosie is often linked. Sometimes, the sisters' invocations of found sounds, back-country spirituals, hip hop and music of the tropics work, and in spades. But their less-successful experiments often seem like poorly wrought appropriations by self-indulging hipsters. To some ears, "Japan" could fall into the latter category.

That dichotomy was confounded by the ill-advised use of a racial epithet on CocoRosie's debut, La Maison de Mon Rave, as well as Bianca's once-regular attendance of Brooklyn's "Kill Whitey" parties, purportedly ironic dance nights in which white hipsters imitate-or parody-hip-hop culture. A Washington Post reporter interviewed Bianca outside one of these parties in 2005. Her take? "It's a safe environment to be freaky."

The Casadys' debut was-at its best moments-charming and warm, like it had been recorded in a womb (though, in fact, they used a Parisian bathroom). But that was always the problem: On their first two albums and the subsequent tours, the Casadys' insular na'vet-they seem so well-fed sometimes, you'd barely believe their tumultuous childhood-was getting them into trouble. They aspired to be worldly, it seemed, but when the songs couldn't deliver, the sisters just sounded ignorant.

With The Adventures of Ghosthorse and Stillborn, they largely avoid that trap by smoothing over the edges. It's a typical pop-music transaction: exchanging idiosyncrasy for consistency, eccentricity for polish.

The finest songs-"Japan," the shimmering and sublime "Rainbowarriors" and the celestial "Miracle," in which Antony cameos-rank among the highlights of La Maison and its follow-up, Noah's Ark. And the lesser numbers avoid the grating, half-thought quality of those early albums' failures; here they're just bland, by-the-numbers trip-hop.

The real highlight is "Werewolf," in which Bianca casually raps and Sierra intones sorrowfully over a bare piano loop. It's an ominous tale of voodoo, cowboys and a father's lessons immemorial. Mostly, it's a blueprint for the type of song that CocoRosie-having grown up significantly-ought to be making more of.

-Jonathan Fischer