It's nice outside, really pretty," purrs a terminally distracted Sierra Casady. "Where it is I'm not exactly sure."

To Sierra and Bianca Casady, the former opera singer and model who are CocoRosie, geography is unimportant.

The American sisters prefer to inhabit their own strange world - a place frequented by fairies and rainbow-warriors, where elected officials are tranny shaman and religious leaders are winged evangelists.

Their latest and third album, The Adventures of Ghosthorse & Stillborn, is a peek inside this demented land set to twisted folk, hip-hop and childrens' toys.

None of which seems so strange once you take into account their unconventional upbringing, which turns out to be as off-the-wall as their faux-naif singing voices.

The Casady's parents divorced when they were young and their summers were spent on the road with their shamanic Cherokee father who dabbled in hallucinogenic drugs.

The sisters were close but Sierra withdrew from the outside world and, at the age of 14, was sent to a reformatory because of her constant singing.

"I was difficult," she admits.

"My mother asked me to leave because I was singing too much. I love my mother, she's really not a bad person, but I didn't talk, I sang and that drove her crazy."

Sierra eventually moved to Paris alone to study opera until, after ten years apart, Bianca showed up.

"It was the last thing I was expecting in the world and so was everything that followed," says Sierra.

"It was really awkward at first - we didn't think of each other in the way we do today - there was a lot of antipathy.

"In the beginning we didn't make music, we made games that we'd play all day," she says, before adding matter-of-factly, "We'd also challenge our telepathic powers and do a lot of squats to release testosterone."

Between the squatting and the games, Sierra gave up on opera after receiving "beatings from fat divas in Rome, New York and Paris".

Instead, the girls recorded their debut, La Maison de Mon Reve, in the bathtub of their creaky Parisian bedsit.

Their latest album was recorded in the marginally more salubrious surrounds of a potato farm in Provence. "We'd kind of creep about unnoticed. We just had an owl and a couple of horses for company."

One of the horses made it on to the album, thanks to the help of Valgeir Sigurdsson, a producer who's worked with Björk and Sigur Ros, and who mixed the album in Iceland.

The Adventures of Ghosthorse & Stillborn is inspired by Wee Willie Winkie ("Childishness is a big inspiration for us") and is named in honour of their elder brother Nathan and their grandfather, both of whom died during its making.

"We carried out their visions and I know I felt them around in a couple of the tunes," she says.

  • Starts 7.30pm, tickets £12. SOLD OUT