The Chieftains may be the best-known folk band from Ireland, but Altan are the best. This is meant as no disrespect to the Chieftains, who dominated the genre in times past and continue to make good music today, but Altan have achieved a musical peak that's impossible to ignore. Because most of their vocals are in Gaelic rather than English and because their instrumental dance tunes stick close to their folk origins, Altan may be less accessible than the Chieftains, but the sheer beauty of the music will reward the patient listener. Two Nashville figures--singer Alison Krauss and dobroist Jerry Douglas--as well as Chieftains flutist Matt Molloy help out on Altan's new album, Runaway Sunday, but the recording is dominated by Altan's co-founder and undisputed leader, Mairead Ni Mhaonaigh, a virtuoso of the legendary fiddle tradition of her native County Donegal. With her quick bow, she is able to articulate each individual note, no matter how quickly it passes by, and to string them together into lines that seem to sing. And when she sings herself, her soprano has the same resonant tone and sure phrasing as her violin. Her five bandmates (who play accordion, bouzouki, second fiddle and two acoustic guitars) follow her so closely that the group seems to move and breathe as one.

Instrumentals, organized into six medleys and a stand-alone piece, dominate, but it's the quality of the songs that make this the most impressive Altan album yet. Ni Mhaonaigh has found a kindred spirit in Krauss, and only a slight Irish accent separates the two singers on an exquisite version of Robert Burns's "I Wish My Love Was a Red Red Rose." Ni Mhaonaigh herself wrote "A Moment in Time" as a tribute to the older Irish musicians who passed the tradition on to her generation, and the lyrics' visual details, the slow, surprising melody, and the breathy vocal all convey an unmistakable affection. The album climaxes with "Time Has Passed," Ni Mhaonaigh's heart-breaking elegy for her late husband and former co-bandleader, Frankie Kennedy. --Geoffrey Himes