<P>Anna Quindlen first visited London from a chair in her suburban Philadelphia home. <P>"'The city streets were filled with fog and the cobbled pavers were slightly slick with moisture, so that the man and woman struggling down the street slid on its surface. It was just after the war, and some of the buildings were empty holes left over from the blitz.' The book describing all this was by Patricia Wentworth, one of a series of mystery novels she wrote that often took place in country shires but wind up always, inevitably, in the capital, at the cozy flat of what I believed at the time to be the essential English spinster."<P>Quindlen has been to London countless times since, in the pages of books. From Dickensian London, rich with narrow alleyways and jocular street vendors, to the London of Conan Doyle and Margery Allingham, with its salt-of-the-earth police officers and crowded train stations. She visited Victoria Station, Hyde Park, Soho, and Kensington in her imagination long before ever setting foot in the city. <P>By the time Quindlen actually visited London in 1995, it was less like an introduction and more like a homecoming. Here, she thought, is where Evelyn Waugh's bright young things danced until dawn. Here is where foolish Lydia Bennett eloped with the dastardly Wickham. Here is where Oliver Twist sought his fortune, and where Adam Dalgliesh has his private flat. New York, Paris, and Dublin are vividly portrayed in fiction, but London has always been the star, both because of the primacy of English literature and the specificity of the city's descriptions. <P>In Imagined London, Quindlen walks through the city, moving within blocks from the great books of the 18th century to the detective stories of the 20th to the new modernist tradition of the 21st. Her book is about traveling and reading in a city in fact and a city in fiction and where and how the two cities intersect.</p>