"He speaks in your voice, American, and there's a shine in his eye that's halfway hopeful".

Aficionados will recognise the terrain from the opening line. Yes, here we are, hacking through the underworld. More accurately, through Don DeLillo's Underworld, his vast and best-selling novel. Page 440 right now, in the Picador edition, read on bus and plane and ferry and train over two weeks and a few thousand miles and half a dozen cities; and close to 400 more pages to read.

This is the way it goes. You plan a trip and you buy a book. You go to Easons or Waterstones or Hodges Figgis or Fred Hanna or wherever and you stand in the vast strange mirror halls of fiction and a choice has to be made.

It must be fiction. You don't read fact when flying. Air-travelling mankind can bear only so much reality. The last thing you want is a critical biography of some important personage to make you feel as small as you really are (which is as big as God has made us, as Paddy Kavanagh noted). And poetry might upset the strange-looking passenger in the aisle seat. There's always one, always in an aisle seat.

So you want to read about things that never happened and never will. Lies and invention. Made-up stories. The created thing. The mental scam. The accepted fraud. The unspoken pact. Paint splashed on a canvas. The visible illusion. Imagination between two covers. First, you browse. You become a browser. Something like a dowser. No, thanks, I'm just dowsing. Looking for something I know is down here somewhere, essential aqua vitae, in this case a decent book. And by the way, no one is ever browsing. You are just browsing. Browsing has an apology built in.

To help choose, you might have scraps of paper, scraps of memory, bits of promises to yourself about what you plan to read sometime. Also in play are your prejudices, admitted and otherwise, your perceived needs, your unrecognised wants and desires.

You pick up a book. A fashionably slim volume, though you know what you want for this journey is something to get a grip on. You want a book with good childbearing hips. So on the cover is a favourable quote by a reviewer whom you know wears lime-coloured shirts and is married to a woman whom you used to think had taste - after all, she went out with yourself for a while. You drop the book without opening it. You have a weakness for American fiction. So you come across John Updike's Brazil, which you never got round to reading. You can still recall the wonder of Couples, read surreptitiously at an inappropriate age. But on the back is a line from Grey Gowrie's review of some time back: "Brazil is a great novelist's solution as to what to do when you are stuck." You see this as back-handed praise. You recall that the patrician Gowrie left British politics because he apparently found it impossible to survive in London on an MP's salary. In a small way you want to get back at Gowrie by buying this book. But you still don't really want Brazil right now.

Threatening and challenging, the vast block pillars of Underworld glower from a table to which you have been gravitating all along. The paperback Picador edition is daunting, a big lump of a book whose visual impact is made with blacks and greys. The cover features an anonymous American city sky-scape with a pale cross-topped church directly in front of a skyscraper disappearing into upper darkness. A single bird, perhaps a dove, hovers in the sky. Inside, the sombre mood is reflected in blank black pages dividing chapters and segments.

The front-cover scene turns out to be a photograph, its reverse image reduced on the back cover, along with a picture of Don DeLillo. Back-cover photographs of authors are often a bad sign, but this one is modest, a simple head-and-shoulders job. Then there are four pages of critical acclaim culled from various reviews of Underworld. Some are suspect, but there are enough reliable names.

The five-line summary of DeLillo's career is succinct. The author does not apparently divide his time between various cities, as seems to be mandatory for so many writers. We do not learn that he once lived in a Mongolian yurt or on a raft on the Yangtze Kyang. It seems he never worked as a mortician's assistant.

All this is encouraging and gratifying. The author has dedicated his book "To the memory of my mother and father." Enough said.

Underworld in this edition has 827 pages. Heft it in the hand. It easily passes the weight test for holiday reading. It costs £10. You know this book has won major awards. You have, contrary as ever, waited to read it until the fuss died down. Now you buy it.

Underworld turns out to be a fabulous, exasperating, sad, nostalgic, upsetting, confusing, challenging, irritating and beautiful story. It has strange lingering echoes of Melville, of Wolfe, of Frost, and even of D.H. Lawrence, and is incidentally as unUpdikean as could possibly be. Underworld is a very fine book, an adventure in language, an elegiac literary voyage. Halfway through, you don't want it to end.