Is a social history of paperback books virtually the same thing as a socio-literary critique of hardboiled detective fiction? Hardly. But O'Brien seems to think so; and his ambivalent focus leads to confusion in this small book (less than 100 pages of text)--which is charmingly provocative when discussing (all too briefly) paperbacks in general, mostly just pretentious (and often off-the-subject) when rambling through a partial multi-media history of the hardboiled genre. The first third of O'Brien's text is highly diverting: he traces the first years of paperback production, from Pocket Books in 1939 (""they fit snugly in the hand"") to the quick arrival of competitors; he distinguishes among house styles; he admires the often crude and lurid paperback-cover art (""to fully appreciate the aesthetics of an old paperback cover, it should be contemplated from a distance of twenty to thirty feet""); he affectionately details the physical, emotional appeal of the books (Dell mysteries ""were a small-scale demonstration of the book as toy""); he enthuses over the Signet covers, which ""found the exact midpoint of American culture. . . something like a twentieth-century equivalent of Currier and Ives."" Then, however, on the premise that hardboiled detection was ""peculiarly identified"" with the paperback format, O'Brien switches to a so-so study of that much-analyzed genre--from Hammett and Chandler to MacDonald, Macdonald, and Spillane--while the paperback theme fades; often, in fact, the essay deals more with movies than books. And when O'Brien winds up, circa 1955, with the hardboiled genre being supplanted by the juvenile-delinquency novel, neither of the two subjects--paperbacks or hardboiled fiction--seems to have been squarely dealt with. This isn't the wry social history of paperbacks it seems to start out to be, then; and mystery buffs can find more clearly focused genre histories elsewhere. But those beguiling opening chapters--and the 100+ photos of often-hilarious paperback covers--are sure to engage unpretentious bibliophiles and those with an interest in pop-culture.