I read and reread the passage for a good five minutes. Surely these references were more than mere coincidence? If so, the horn in the decrypted verse referred to the harbour at Constantinople, to what was now called Istamboul: a harbour also known as the Golden Horn. And it did so especially when one took into account the other, wholly unexpected allusion to the harbour named 'Under the Fig-tree'.

But these discoveries, like the actual decipherment, led to no immediate answers, nor prompted any further ideas. The reference to ancient Byzantium did not exactly elucidate the four lines, much less untwist the labyrinth; nor did it explain why the Golden Horn-a body of water-was called a 'fabric', as if it were a tapestry or even possibly a building. I could only begin to guess why the intricately coded verse between the pages of an edition of Ortelius appeared to lead to a quotation describing the meeting-point of two continents, a harbour some fifteen hundred miles distant from Pontifex Hall. At the time I had no idea whether Sir Ambrose had travelled as far as Constantinople in his quest for books, though I seemed to remember how one of the patents granted by the Emperor Rudolf-one of the dozens of parchments in the coffin at Pontifex Hall-had been for a voyage into the lands of the Ottoman Sultan.

So, as I ate my kippers, I wondered if the cipher had something to do with Sir Ambrose's library, or even with the missing Hermetic manuscript itself. It was impossible to be certain on so little evidence. But I decided the manuscript might well elucidate the verse, and so before I had finished my breakfast I was resolved to venture outside in search of it.

But my elation soon disappeared, for my quest among the shops and stalls proved as unhelpful and unpleasant as I feared it would. In Smithfield the stench had become so overpowering that as the orphans in Christ's Hospital began their first lesson of the morning the sashes in their classrooms were lowered despite the heat. Beneath the Hospital's east wall the booksellers in Little Britain had draped their windows with curtains soaked in chloride of lime. As I arrived they were holding handkerchiefs to their noses and setting out stalls of books whose covers would have to be dusted of soot three times before the working day was over. But after three hours of poking round in these stacks I had succeeded only in tiring my feet, burning my nose and neck in the sunlight-which was scorchingly hot whenever the coal smoke cleared enough to admit it-and attracting blank stares from disinterested shopkeepers who claimed never to have heard of either a book or a manuscript called The Labyrinth of the World.

A pint of Lambeth ale at lunch revived me, and I caught a hackney-coach to Westminster Hall, where, of course, I had no better luck than in either Little Britain or Paternoster Row. Yet the day was not an utter loss, for I did manage to learn something about the Prague edition of Ortelius's Theatrum orbis terrarum, though nothing that seemed to chime with anything I had so far discovered about either Sir Ambrose Plessington or his missing parchment. All of the booksellers and stallholders stocked copies of the Theatrum, and one even held the rare 1590 edition printed in Antwerp by the great Plantinus. But none had ever heard of the Prague edition, much less sold it. They were as puzzled by the edition as I had been. I therefore decided I must have misread the tailpiece; either that, or the 1600 edition was a forgery. I was about to return home, when I spotted, beneath the arcade of the New Exchange in the Strand, the shop of a map-seller, Molitor & Barnacle. I knew the establishment well. As an apprentice I always found it the most intriguing shop in London, for in those days I still dreamed of travelling the world, not fleeing from it, as I do now. Despatched on an errand by Mr. Smallpace, I sometimes used to duck inside and browse for hours among the maps and metal globes, my task completely forgotten until Mr. Molitor, an indulgent old soul, would chase me from the premises at closing-time.

Now it was almost closing-time as I stepped through the door to see that most of the globes and astrolabes had disappeared, as had the maps of the world, beautifully engraved reproductions of Ptolemy and Mercator that Mr. Molitor would pin to the walls like charts in the cabin of a ship. Eight or nine years must have passed since my last visit. Mr. Molitor, alas, had also disappeared-dead of consumption in '56, I was told by Mr. Barnacle. I was sorry to see that the shop had fallen on hard times and that Mr. Barnacle, now an elderly gentleman, failed to recognise me. Seeing him stooped behind his counter, breathing heavily, I had a chastening vision of myself twenty or thirty years hence.

But Mr. Barnacle knew his business as well as ever. He informed me that he knew of the Prague edition of the Theatrum but had never actually seen a copy. They were, he explained, exceedingly rare and even more valuable than the editions published by Plantinus, for only a very few copies had ever been printed. But this scarcity was not the sole reason for their great value. The edition was the first posthumous one, since Ortelius had died a year or two before its appearance. He was Flemish, suspected of Protestantism, but for a quarter of a century he had been Royal Cosmographer to the King of Spain. After Philip's death in 1598 he travelled to Prague at the invitation of the Emperor Rudolf II, but died before he could take up his post as Imperial Geographer. Mr. Barnacle alluded to a legend among map-makers, thoroughly unsubstantiated, that he had been poisoned. The Prague edition appeared a year or two later. The legend further suggested that it included some sort of variant, though Mr. Barnacle could not say precisely what. But it was for the sake of this new detail that the great cartographer was murdered.

'A variant? What do you mean?'

'I mean that the 1600 edition was different from all of the other editions, including those printed by Plantinus. Mr. Molitor had his own theory about it,' he said in a confidential tone, producing from his shelves a copy of the atlas. When he opened the cover I could see a plan of the Pacific Ocean and, inside a cartouche, the words NOVUS ORBIS. 'It involved the particular method of projection that Ortelius uses for the Prague edition.' He turned round again, suddenly spry, and reached down another text. The scale of latitude and longitude. 'All of the other editions use Mercator's projection. You know about the Mercator projection?'

'A little.' I was watching as he creaked open Mercator's famous atlas-an atlas whose maps I used to study with especial delight during my daydreaming apprenticeship. I am not mathematically inclined; far from it. Words, not numbers, are my métier. But I was able to appreciate a little of Gerardus Mercator's feat in representing a sphere, the earth, on a plane; in flattening the world and putting it in a book, its proportions more or less intact.

'His projection was created for the sake of navigators,' Mr. Barnacle was explaining as he tapped one of the sheets with a cracked yellow fingernail, then readjusted his spectacles-a pair with lenses almost as thick as my own-on the bridge of his nose. 'It was devised in 1569, during the great age of exploration and discovery. His scales of latitude and longitude form a grid of parallel lines and right angles that make it possible for mariners to plot compass courses along straight lines instead of curves. Most helpful, of course, for voyages across the ocean.'

He was tracing a thumbnail diagonally across the sheet, along a thumb-line that stretched like a spider's web across a grid of squares. Then abruptly he pushed both atlases aside and reached for one of the globes, an enormous paste-board model, some four feet in diameter, which he spun on its lacquered pedestal. Blue oceans and mottled land masses flashed past beneath the brass horizon-ring on the equator.