It would be very easy for CocoRosie to make merely ornamental music and focus only on the pretty, ethereal sound that was so charming on La Maison de Mon Rêve.

Fortunately, Sierra and Bianca Casady have more ambition than that, and they've managed to craft very different identities for each of their albums -- no small feat, especially since their approach is so distinctive.

On The Adventures of Ghosthorse and Stillborn, they combine the cleanest, most polished-sounding production to appear on a CocoRosie album with a stark hip-hop influence, making this the duo's most focused, and strangest, album yet.

The sisters explore this polarity throughout The Adventures of Ghosthorse and Stillborn, opening the album with the bold, jaunty beats of "Rainbow Warriors" and following it with the much more delicate trip-hop of "Promise." Switching back and forth between mischievous, endearingly awkward moments and one of breathtaking beauty like day and night, or waking and dreaming, it's almost as if the album posits each of the Casadys' talents as opposing viewpoints.

The tracks Bianca takes the lead on are bright and outrageous, like "Japan," which bounces along like the Mad Hatter's tea party as she sings, "Everybody wants to go to Iraq/But once you go there, you don't come back." The song's topsy-turvy feel only deepens when Sierra's eerie background vocals turn into a cheery trumpet melody.

Meanwhile, "Black Poppies" and the other songs Sierra dominates delve even deeper into the narcotic chansons of La Maison de Mon Rêve and Noah's Ark.

Her singing on The Adventures of Ghosthorse and Stillborn is her finest yet, especially on the middle-of-the-day lullaby "Sunshine" and "Miracle," where she has much more power and range than some of her previous kitten-ish Billie Holiday impersonations would suggest.

The playful arrangements that are so vital to CocoRosie's sound come into sharper focus on this album, too, with a toy box's worth of sound effects adding poignancy and whimsy to "Animals" and harp and trumpet deepening "Raphael"'s mournful beauty.

The Adventures of Ghosthorse and Stillborn's densely packed sounds and ideas are a lot to process, but they're what makes this album rewarding on repeated listens -- and what makes CocoRosie's yin-yang, fractured fairy tale sound still surprising three albums into their career.