Disco diva Sylvester an imposing androgyne who scored Top 40 hits like ''You Make Me Feel (Mighty Real)'' in the late '70s was an almost indescribable figure: the outré outfits, the high-pitched falsetto, the sequined everything. In The Fabulous Sylvester Joshua Gamson writes about the singer's offbeat life in San Francisco with the excitement of an archaeologist screaming ''Eureka!'' at every turn; his prose is playful and furious. Putting the singer's story into sociological context, Gamson recounts the rousing Sundays of his churchgoing youth in L.A., which influenced his wild stage shows. He rightly conflates the emergence of disco and the backlash that followed with the civil/gay/women's rights movements. And he captures the astonishing scope of AIDS with grace and indignation, portraying Sylvester's death in 1988 as if amazed that such a force of nature could ever be defeated.