Alison Krauss is on tour this summer with former Led Zeppelin vocalist Robert Plant, an odd couple if ever one existed. She, after all, is known for an ethereal vocal quality, while he was the shrieker on such classic rock hits as "Black Dog" and "Stairway To Heaven." Adding to the unlikeliness of their musical pairing, there’s quite an age difference: She was born in 1971, at a time when Zeppelin had already released three albums.

But to hear it from Robert, Alison was a logical singing partner.

"It’s all about restraint," he told The London Times, noting that he’d pretty much hit the pinnacle as a hard-rock wailer. "Where do you go next?"

Nashville, apparently. Not only did the Raising Sand album land them on the GAC Top 20 Country Countdown, they actually rehearsed their tour at Music City’s Sommet Center, the home of the Nashville Predators hockey team.

"What a place for me to land," Robert laughed. "Look — I’ve got new cowboy boots, and these flares are great: They’re a 33-inch waist, and they’re ladies’ jeans."

That raises a not-so-obvious question: Which of the two artists wears the pants in their unexpected collaboration?

"Depends on what day it is," Robert replied. "She puts up with some of my rather lewd English stuff. And I have to wait for her to get ready. That kinda balances it out a bit."

Alison, for the record, does not dispute that assessment.

"That’s fair," she said. "I am tardy!"

Touring with a band that includes producer-guitarist T Bone Burnett, Robert and Alison are currently in the United Kingdom. They’ll play Europe throughout the month, returning to the U.S. in June with a show in Virginia Beach.