IN THE EARLY '90S, while an entire generation of Beat Happening fanatics were making the simplest music possible, Polvo was dirtying things up. Employing a distinctly low-key sound (every track sounded as if a layer of fuzz was applied), yet playing mysteriously jagged, minor-key discordance that smacked of good musicianship, Polvo eschewed the fresh-off-the-street sound so popular at the time. As Calvin Johnson became the king of two-note lo-fi, Ash Bowie, guitarist, vocalist, and leader of Polvo, became an indie rock godhead.

Polvo broke up in 1997, and Bowie retreated to play bass full-time in Helium, whose last album, The Magic City, was defined by commanding, arpeggiated guitars and fairy themes. Bowie and Helium's founder, Mary Timony, seemed to be a match made in Legoland, both through their innovative approach to guitar and affinity for the otherworldly.

If this year's Mountains, Mary Timony's first solo album, was the unicorn's tear--delicate and saturated with mystical, crystal love--then Ash Bowie's first solo effort (as Libraness) is the ready-for-battle gnome dance, complete with satyrs dancing around fires.

Yesterdayand Tomorrow's Shells consists of 14 primal/cerebral songs Bowie's been brewing since 1993. It's filled with his signature guitar work: tough-ass, classically trained, classic rock riffs rendered off-kilter by distortion; foreboding, mandolin-sounding war cry melodies. Some songs sound as if they're outtakes from Polvo's imperative first album Cor-Crane Secret; others seem descended directly from Helium's parallel universe.

Most interesting is Bowie's austere, crackling interplay between the edge of prog and cyber-real battle themes. Progressive rock, underrated and overshadowed in its time, seems to be the exact logical nexus of where indie music is going in the 21st century. The parts where Yesterday falls short is on those few songs that take the castle/dancing-ladies-feasting-on-boars themes too far. What will make prog successful this time around is that musicians like Bowie and Timony adhere to the idea that, while guitar virtuosity can sound very cool, too much D&D never did a kid any good. Conservation of noodle riffs is key. Bowie does it, for the most part, combining his tactical punk with technical guitar and a smoky voice that always sounds like he's telling secrets. You can almost hear him whispering now: "Get ye a King Crimson record, youthful serf."