For some bands, losing a member is no big deal—you either replace the person or just do without that second rhythm guitar or whatever. But for young British band the xx, the recent loss of guitarist Baria Qureshi posed more of a problem—for one thing, the band already possessed an intently austere sound from which not much could afford to be subtracted; for another, they'd all been friends since childhood.

"We've been friends with Baria collectively since we were 11," says xx covocalist and multi-instrumentalist Romy Madley Croft, now 20, by phone from a tour stop in Chapel Hill, North Carolina. "But you grow up, and sometimes you grow apart from your friends."

Croft and singer/bassist Oliver Sim have in fact been best friends since the age of 3 ("kindergarten, you call it here," she says). They began making music with Qureshi and programmer/producer Jamie Smith while attending and on holiday from South London's public Elliott School (which also produced such similarly introverted beat-makers and songwriters as Burial, Hot Chip, and Four Tet). In August, the xx released their self-titled, two-years-in-the-making debut on XL imprint Young Turks to overwhelming critical praise. (The band worked with producers such as Diplo, Lexx, and Kwes before deciding to go it alone in the studio and record the album themselves.) If some slow drifting apart with age is inevitable, the band's sudden success and subsequently hectic touring schedule (they played, like, 40 shows at CMJ) rapidly accelerated the process.

"We've never done intense touring before," says Croft. "I think being together all the time brought to a head that maybe the social aspect of the band wasn't working. It was kind of a sad realization, that maybe we'd grown apart and maybe it wasn't working as well as it had in the past."

The band canceled a handful of European shows due to exhaustion at the end of October, and when they resurfaced for gigs in London and New York, they were shy a member. They soon announced that the band would not be seeking a replacement.

"I'm really positive about having a three piece," says Croft. "It's been exciting. We've always been more into jamming and being more improvised, so we're going to push with that and keep going."

"We're working it out," says Croft of the newly reduced lineup. "We had about a day to work it out when we came back to London, because we didn't want to cancel more shows, but we didn't want the shows to come off half-assed. Jamie plays more on the MPC; I play keys and some more guitar parts. We're very keen to keep it 100 percent live, as well. We've never been a fan of backing tracks or anything, so we're just working a little bit harder now onstage."

Listening to the xx's softly stunning album, you might rightly wonder how they could possibly lose a thing from their sound and still carry on. Maybe the most defining feature of their songs is space—space between notes and beats, space implied by cold reverb or close quarters suggested by hushed singing voices, the distances explored in the band's lyrics and emphasized by their girl/boy delivery. Anything less and you'd risk opening up a black hole.

The guitars and bass recall early New Order, back when that band still sounded totally hollowed out by the loss of Ian Curtis. But Smith's beats and the group's vocals are something else—the former muted, bedroom-bred stuff à la fellow Elliott alums and upcoming tour-mates Hot Chip; the latter intimate, indoor-voice singing shared between Croft and Sim that has more to do with breathless R&B than it does with anything remotely post-punk.

Croft and Sim's duets exude a sensual, often sexual tension, especially when one or the other or both of them are cooing lines like "I am yours now," "I still need you," "I can't give it up to someone else's touch," or "I think I'm losing where you end and I begin" (from the songs "Islands," "Heart Skipped a Beat," "Infinity," and "Basic Space," respectively). But Croft insists that the lifelong friends aren't aiming their words at each other.

"I can see how there'd be a tension about a girl and a boy singing, but it's always an outside figure that we're addressing," says Croft. "Our lyrics kind of interlock around a theme, sort of sharing the songs, but we're not actually addressing each other. I like that there's an ambiguity there, that we could be singing to each other, but it's never actually the case."

Still, that tension fills the album's spaces with an electric charge, animating the deceptively quiet songs. And deeper listens reveal plenty of subtle rhythmic action and addictive melodies. There are parts of this record that you just can't shake—that willfully wimpy keyboard on "Basic Space," the way the bass follows the guitar on "Islands," or how that song pivots when Sim joins Croft for one line before taking over for the second verse. All of which helps enliven the band's fittingly withdrawn live show, which features all members standing stock-still at the front of the stage while singing or playing their instruments.

"We started gigging when we were 17," says Croft. "But I think that, generally, as people, we're not the most born for the stage. So it has been a long process for us, just gaining the confidence to perform and be up there. It's still a work in progress.

"But," she concludes, "if I was jumping up and down during, like, 'Shelter,' I'd look insane."