Sky & Country (on the ECM label), the new CD by Fly—the trio that consists of saxophonist Mark Turner, bassist Larry Grenadier, and drummer Jeff Ballard—is a deeply pleasurable album. It’s a tricky thing to improvise sinuous, crisscrossing lines over the span of an hour-long record, with neither a piano to lay down harmonic signposts nor a second horn to pick things up when the pace slacks off, yet still manage to keep a listener’s attention. Some have done it, and brilliantly: Sonny Rollins (A Night at the Vanguard and Way out West), Lee Konitz (Motion), Ornette Coleman (At the Golden Circle and Sound Grammar), and David Murray (The Hill), among others. But this list only amplifies the scope of the challenge. Sky & Country is nothing like any of those albums, but it’s harder to describe what it isn’t than what it is. It doesn’t have much in the way of distinct melody, but neither is it the slightest bit atonal. It’s low key but not mellow, cool but not insouciant. Turner plays the sax in a style reminiscent of Warne Marsh: without vibrato, even-keeled, endlessly inventive but not at all showy about it. (Josh Redman and Branford Marsalis also have pianoless-trio albums out now, but among the three Turner is the only one who doesn’t resort to riding scales or extending arpeggios when he gets stuck in a spot; he always finds ways in and out without lapsing into clich.) Grenadier and Ballard are the bassist and drummer in Brad Mehldau’s piano trio—which is to say they can take anything and shoot it right back while supplying support. Fly is as pure a jazz trio as I’ve heard in a long time; no player dominates, all contribute equally but in very different ways; the strands stream off in several directions at once, yet they seamlessly cohere, like some musical equivalent of superstring theory. I can’t figure out quite how they do it, but they do. The sound quality, by engineer James Farber, is superb: tonally true with plenty of airy ambience.