Plant Krauss at Greek

The genre of pop standards is a bit out of bounds for Robert Plant and Alison Krauss, whose high-profile collaboration excavates a more traditional sector of America's musical geography. But when the singers and their band came to the Greek Theatre on Monday, there was something of “The Wizard of Oz" about it.

The roles are a little scrambled, but picture Plant as an English rock-star version of Dorothy, a noble, curly-maned lion who has entered the swampy heart of American blues and country after decades of flirting with it from afar, both as the singer of Led Zeppelin and as a solo artist.

The pilgrim is accompanied by a muse of singular voice and vision in country/bluegrass star Krauss, and a tall, eccentric scarecrow who's actually pulling the strings -- guitarist and bandleader T Bone Burnett, whose selection of songs and musical concepts helped transform what began as a tentative teaming into a fertile enterprise.

It's one with a broad reach and a cutting edge. “Raising Sand," their album from last fall, has found critical acclaim and a substantial audience, and on the first of their two nights at the Greek, the outdoor theater was packed with both Americana enthusiasts and weathered rock warriors in vintage Zeppelin T-shirts.

On stage, it all clicked on multiple levels: the back story (two celebrated, not obviously compatible artists get together for purely creative reasons and make a go of it), their distinctive voices, the stories told in the songs, the rapport of the five instrumentalists (six when Krauss played fiddle), the underlying tension of thousands of people hoping that Plant would dust off a Zep classic.