Vice Versa, by Marjorie Garber (Penguin, Pounds 12 99 in UK)

Bisexuality is seldom treated as anything other than a joke, hut Marjorie Garber has made so thorough a study it that by the end of her 600 paperback pages you find yourself thinking about sexuality in a totally different way - which is OK by her, since her thesis questions the whole concept of polarised sexual identity, substituting instead a "shaded spectrum" idea which would have been familiar to the ancient Greeks. The book may not sound like a barrel of laughs, but her extensive use of literary and cinematic quotation, and her obvious expertise on, of all things, Shakespeare, brings unexpected depth and interest to what might seem a rather slight topic.