Now this is how it's done, and by this I mean bluegrass for the 21st century. Not, mind you, that there's anything wrong with those other bluegrasses. I have loved them long and with careless abandon. And I suppose it's because I love them -- and by them I mean Bill Monroe, Ralph & Carter Stanley, Flatt & Scruggs and all their many spawn -- that I fear, as bluegrass changes as all things must, it will abandon its fundamentally rural character in a century when "rural character" will be an ever more distant, sentimental memory.

Della Mae is not one woman but four, all of whom have last names. Though young, they lay claim to a formidable body of experience in bluegrass, old-time and folk. These influences are wed into a music both passionate and meticulously fashioned, with rhythm guitarist and principal songwriter Celia Woodsmith the most out-front presence. The others are fiddler Kimber Ludiker, bassist Amanda Kowalski and mandolinist Jenni Lyn Gardner. The band is based in Boston, but it plays in many other places. When its travels take it to a bluegrass or folk venue near me, I'll be there. If these women are this good on record -- and I Built This Heart will be among the unforgettable bluegrass discs you hear this year -- they must be fabulous on stage. That's not just a wild guess, by the way; that's based on what I infer from seeing them at a live gig captured on a YouTube video.

Another thing: as women have come to prominence in a once male-dominated genre, their models tend to be Alison Krauss and Rhonda Vincent. Krauss and Vincent are very good at what they do, but theirs is as often as not a sweetened sound, sometimes too sweet for bluegrass as such to handle. This is especially true of Krauss, who is (as is her right) wandering more and more into a self-invented acoustic genre, taking with her the young female performers who are her acolytes. It's the sort of approach that I respect without listening to much (which by now, I confess, describes a fairly substantial quantity of music). Vincent is enamored, as I am not, of contemporary Nashville country-pop. Della Mae, on the other hand, has a sound as distinctive as Krauss's, and in some ways as modern as Vincent's, but less equivocally linked to a tradition of mountain bluegrass, if not in the pure, hard-core style of, say, Hazel Dickens and Cousin Emmy.

Speaking of whom: The two non-originals here are Dickens's "My Heart's Own Love" and Cousin Emmy's variant of the folksong "Bowling Green." The Della Maes (if I may) make each their own, which means the downhome background is omnipresent without being defining; city and country meet at the outskirts of town, you might say. Dickens and Cousin Emmy, both gone from us (Dickens just this year), would have heartily approved, I suspect.

Of the originals, the most tradition-like is "Ballad of a Lonely Woman," recalling the high and lonesome Appalachian sound. On the other side of the hill is "The Most," the most erotically charged bluegrass song I have ever heard. Actually, when I think about it, the only erotically charged bluegrass song I have ever heard. The other songs, conjuring up stark scenes of life and death, are delivered in Woodsmith's unflinching, almost uncannily assured vocals, supported by the band's no-prisoners trad/modern harmonies: "Aberdeen," "Aged Pine" (from which the CD title is taken), "Verona" ... wow, now that's some chills up the spine.

Is it possible Della Mae could be even better next time out? Or is that too scary to contemplate?