By Marc Atkins and Iain Sinclair

Reaktion. 223 pp. Paperback, $29.95

Not all tourists are created equal. Any map is only one version of reality. Thus the official set of London myths and monuments that most visitors encounter as they go about checking off Important Landmarks and Major Museums hardly exists in the same universe as the psycho-geographical concerns of Iain Sinclair. A novelist-poet, sometime secondhand book dealer and serial walker, he's also a busker of urban insights who's made the entirety of London, but especially its less manicured precincts, his pitch.

"Liquid City"--the title invokes the ineluctable Thames--is a formless sequel to his previous book, the exhilarating and thoroughly seductive "Lights Out for the Territory" (1997). Subtitled "9 Excursions in the Secret History of London," that volume, an eccentric personal Baedeker, ignored Harrods for Hackney and escorted us, among other outings, to gangster Ronnie Kray's funeral, an event that surely rivaled Diana's for floral tributes and overexcited media coverage.

As he drifted "purposefully" across the city in that earlier book, "noticing everything," Sinclair called to mind Henry Mayhew, the 19th-century chronicler of the London poor, but a Mayhew channeled through, say, Tom Wolfe. And like W.H. Auden, who reportedly favored hikes past the gasworks and rubbish dumps of Oxford, Sinclair seemed to feel a gravitational pull to neighborhoods in more unpicturesque zones, places where the city lets down its guard and gives us clues to its unsought secrets.

At the same time--and often on the same route--he frequently paused to pay homage to equally neglected or esoteric literary figures (Emanuel Litvinoff, Aidan Andrew Dun, David Gascoyne, etc.). "Back-catalogue writers," he called them, or, more hauntingly, "the vanished who don't yet know it." But their presence--they served as avatars of a cult of antihero worship--lent an extra weight to the goings-on. The rewards turned out to be greater, in human terms, than just a day of kicks.

Like "Lights Out," "Liquid City" wasn't written for the average tourist. That is to say, the uninitiated don't head casually to Victoria Park or Woolwich Common; and even the adventurous, eager to broaden their horizons, may lack the proper sensibility to appreciate "the diesel fug of the stampede towards the Blackwall Tunnel." Still, it's hard to imagine loving London and finding nothing in either book that doesn't arouse a primal envy of Sinclair's easy intimacy with it.

Photographer Marc Atkins, who contributed an eight-page picture insert to "Lights Out," is handed top billing in "Liquid City," and his witty, almost peepshow-in-reverse images do dominate its pages. But Sinclair's recent, larger fame makes that act of name placement just a generous gesture, really, since it is sure to be his fans the book will attract. Though the two friends share a unified vision, without the spark of Sinclair's prose the book would never fully flame into life.

One thing is clear, and that's that with or without our encouragement, Iain Sinclair would be on the move. Inventively practicing an alchemical synthesis of "magic and feet," he lights out each time with the intention of decoding the messages imprinted--visibly or invisibly, it doesn't matter--on London itself. Such "whispers from tired stone" are what we look to him to interpret.

And what we thrill to when he does.