The Dresden Dolls, Academy, Birmingham<br/> Mystery Jets, Electric Ballroom, London

Psst! Wanna buy some stripey tights?

'This is the strangest job in the world," Amanda Palmer muses mid-set. "You watch a human being faint six feet away from you, and you have to pretend it's not happening." There can't be many piano-based acts who could cause their fans to pass out in hysteria, but there aren't many bands like The Dresden Dolls.

The stealthy rise of this extraordinary Bostonian duo is one of the most heartening developments of the decade. With no airplay to assist them, no TV and precious little press, Palmer and her sidekick Brian Viglione have managed to initiate a snowball of word-of-mouth recommendations, and inadvertently inspire a whole subculture inspired by their "Brechtian punk cabaret" aesthetic. Teenage gothic ragdolls and middle-aged bohemian aesthetes: you'll find all types in a Dresden Dolls audience. It's a wonderful sight.

With her whey-white face and stripey tights, Palmer resembles Jemima from Play School, and with his bowler hat and clown face-paint, Viglione looks like a Pierrot doll gone a bit Clockwork Orange. Together, they're The Carpenters reanimated by Tim Burton.

A jazz-trained percussionist and a classical pianist, the temptation to indulge in muso excess must be immense, but the Dolls shun that route, instead choosing to pursue a sound that's both baroque and brutal, and seemingly far too big to emanate from two humans with only a drumkit and a keyboard between them.

Despite their Massachusetts origins, The Dresden Dolls are a profoundly European band. Their music and performances have the atmosphere of 19th-century phantasmagorias and Grand Guignol stage shows.

Much of tonight's show, however, hinges on the more humanistic new album Yes Virginia, and some judiciously chosen cover versions, with Viglione crawling from behind his kit to play guitar while Palmer steps forward to sing T Rex's "Cosmic Dancer" and "Amsterdam" (mistakenly attributed to "French singer" Jacques Brel, but we'll let the angry Belgians dispute that one).

After a rendition of "Half Jack" so epic that they appear genuinely drained afterwards, it's time for their greatest hit. "Girl Anachronism" - a stay-away warning from the point of view of an unstable psychiatric case - is perhaps their most misunderstood song. A generation of self-absorbed girls have adopted it as their anthem, but I'm half-certain that the joke's on them.

The best, it seems, is yet to come. Amanda returns for a solo encore "Ampersand", an unreleased new song about not wanting to be someone's plus-one. She's rejoined by Viglione for Sabbath's "War Pigs" (in Ozzy's home town), the drummer leaping up dramatically to play the overhead air vents.

Then The Dresden Dolls walk forward, clasp hands for a curtain-call bow, as if this is the theatre. Scratch that - what do I mean "as if"?

"When were these guys big?" asks a friend I've dragged along to see Mystery Jets, blissfully ignorant of their vintage. When I tell him they're still on the way up, he's amazed.

Mystery Jets are fresh meat: sedentary singer and multi-instrumentalist Blaine Harrison (pictured, right) is young enough to have been locked out of his own aftershow on a recent visit to New York.

Well, almost all of them. The keyboardist to his right, with the white Tony Hart locks, is his 55-year-old dad, Henry. This is just one way in which the Jets are peculiar.

It would be patronising, and probably incorrect, to assume that Henry Harrison is entirely responsible for the archaic influences in Mystery Jets' sound, but it's definitely there.

One way or another, there's something impeccably British about them. Debut album Making Dens has a strong flavour of the eccentric end of prog: Bonzo Dog Doo Dah Band, Alex Harvey, and The Who's stranger moments. Indeed, some of their material delves into an era before rock altogether, with mournful sea shanties and drunken jigs.

Just when you're thinking that Mystery Jets are the kind of band who'd probably play a dustbin lid, there's a stage invasion, the lights come up, and you notice that they are playing a dustbin lid. A pink one.

A more pertinent question, given the Mystery Jets' intrinsic strangeness, might be "Why are these guys big?" Then again, as the rise of The Dresden Dolls illustrates, British audiences have a good record for that kind of thing.