Like Thea Holme's admirable Chelsea (p. 111) an invaluable companion for the London visitor, and although Mackenzie does not linger as long at way stations as Miss Holme did, he has much more territory to cover. For the area called Marylebone (a packed parallelogram in north London) has, unlike Chelsea, ""no clearly defined social image. It is merely a topographical fact."" For the contemporary tourist the area -- now incorporated into City of Westminster -- sports the zoological gardens bordering on Regent's Park, Madame Tussaud's, the BBC, and Baker Street to which Sherlock Holmes pilgrims come for wild surmise. Marylebone was pretty much of a village until the reign of George II, and much of the district retains a Georgian classic tone, with a fillip of Regency influence near the Park and Victorian accents around what used to be the ""hideaway"" villas of St. John's Wood as well as glimpses of some famous inhabitants. Dickens entertained lavishly -- too much so thought Mrs. Carlyle ("". . .pyramids of figs, raisins, oranges -- ach!""). Or George Eliot bouncing through Regent's Park with Lewes: "". . .she with a certain weird sibylline air. . .swinging their arms. . ."" Authors, artists, merchants of note, Americans (including Benedict Arnold), French emigres, rakes and bawdy houses -- it's a good show. There are a number of architectural observations including a not-too-dismayed view of the future. Photographs throughout, but sadly, the only useful contemporary map bears the legend -- ""sites now demolished."" Rewarding but more for the traveler on a leisurely Cunard than a 707.