Twenty years after its release, Phish's double-CD collection A Live One has something rare and precious going for it: it still doesn't sound like anybody else. Oversized, perverse, requiring an unusual amount of listener background knowledge? Yes to all. Yet the collective improvisations it captures, unprecedentedly coherent yet freewheeling and open-ended, are unique in rock 'n' roll.

This book considers the music and moment of Phish's ecstatically inventive 1995 live document, a mix of weirdo acid-psych, ambient moonscapes, vaudevillian Americana, and riotous arena-rock...