And it is at this point, in Alexandria, that the stream widens to Nilotic dimensions. From the great Library the texts spread outward to every corner of the ancient world, and for the next seven hundred years no respectable treatise-no matter whether its subject was astrology, history, anatomy or medicine-would be complete without a few choice references to the Egyptian priest whose revelations everyone agreed were the wellsprings of all learning. But then, after so much expansion, the river suddenly contracts. The stream slows, thins, divides and-after the rule of the Emperor Justinian, who closed the Academy in Athens and burned the Greek scrolls in Constantinople-disappears. The Hermetic texts are not heard of again until several hundred years later. At this point, early in the ninth century, copies turn up in the new city of Baghdad, among the Sabians, a sect of non-Muslims who had migrated from northern Mesopotamia. They proclaimed the revelations of Hermes as their Holy Scripture, and their greatest writer and teacher, Thabit ibn Qurra, refers to the Sabian texts as a 'hidden wisdom'. But some of this wisdom must not have been hidden all that well, because it soon made its way into the hands of the Muhammadans. Mention of Hermes Trismegistus can be found shortly after Thabit's time in the Kitab al-uluf by the Muslim astrologer Abu Ma'shar, and a Hermetic text, The Emerald Table, part of a larger work known as The Book of the Secret of Creation, is studied by the alchemist ar-Razi.
But soon after the time of these Arab writers the stream had thinned and disappeared from Baghdad, again for political and religious reasons. After the eleventh century a strict Muhammadan orthodoxy was imposed throughout the Empire and no more is heard of the Sabians of Baghdad. However, the Hermetic works reappear almost immediately in Constantinople-the city alluded to in the cipher-where in the year 1050 the scholar and monk Michael Psellos receives a damaged manuscript written in Syriac, the language of the Sabians. And it is one of these manuscripts, copied by a scribe on to parchment, then removed from Constantinople after its capture by the Turks, that is brought to Florence, to the library of Cosimo de' Medici, some four hundred years later.
But where did The Labyrinth of the World fit into this long and complex history? I could find mention of the book neither among the editions nor in the commentaries on them-and not even in the Stromateis of Clement of Alexandria, who lists the names of several dozen sacred works written by Hermes Trismegistus. It seemed that The Labyrinth of the World was even more mysterious and shrouded in secrecy than all of the other books.
Discouraged, I therefore chose a different tack, catching a sculler to Shadwell in order to visit the paper-mill of John Thimbleby. I had done business with Thimbleby for many years, and he proved to be, as I suspected, the 'JT' of the watermark on the interfoliated leaf. But he was unable to tell me either when precisely the mysterious piece of paper was made or where it might have been purchased.
The specimen was, Thimbleby admitted, an inferior effort. Did I see how flimsy the paper was? How it was already yellowing and curling? How it was almost transparent when held against the light? This meant it might have come from a batch made in the 1640s, probably between 1641 and 1647. During those years Thimbleby was mainly but not exclusively supplying Royalist printing-presses, including the King's Printer, who had been trailing the thinning and beleaguered Royalist armies round the country and cranking out their propaganda as soon as it could be written. The paper was of poor quality in those days, he explained, because demand had drastically outstripped supply.
Thimbleby took me into his workroom, where two men were dipping frames into a giant vat of what looked like porridge. Paper was usually made in this way, he explained as he gestured at the porridge, which a third man was endeavouring to stir: from linen rags, scraps of old books and pamphlets, various other oddments collected by the rag-and-bone men. These were cut into strips, shredded, boiled in a vat, marinated in sour milk, fermented for a few days, then strained, like so, through a wire mould-mesh. But with the shortage of linen scraps came improvisation. Seaweed, straw, old fishing nets, banana skins, hanks of rope, even cow dung and rotted burial shrouds from the skeletons exhumed for burning in the charnel-houses-Thimbleby had been forced to make use of almost anything. The result was paper of a dubious quality, which he nevertheless sent to the Royalist armies. Checking his records, he was able to tell me that large consignments had been shipped to Shrewsbury in 1642, to Worcester and Bristol in 1645, and to Exeter in 1646. But he had manufactured hundreds of reams every year, from any one of which, he told me, the mysterious page might have been taken.
And so I had returned to Nonsuch House that evening with only a vague clue as to when Sir Ambrose might have encrypted the verse. Still, Thimbleby's account was encouraging. If the verse had been encrypted in the 1640s, at the outbreak, or even during, the Civil War, my theory made sense. The cipher must make reference to a treasure, including perhaps the parchment, which had been hidden-at Pontifex Hall or elsewhere-and was meant to be recovered once the Parliamentarians were defeated and it was safe to return to Pontifex Hall. But the treasure had not been recovered. Why not? Because Sir Ambrose had been murdered, as Alethea claimed? But murdered when? I realised I didn't know when Sir Ambrose died. It must have been before the end of the Civil War in 1651, when Pontifex Hall had been expropriated, but I couldn't remember Alethea's having said.
Before slipping the page back beneath the floorboards I had studied it for a moment, holding it to the light of the candle, looking first at the watermark, then at the close-set lines, the slight impression of the mould-mesh criss-crossing the surface. I thought of Thimbleby's disquisition and wondered what exactly this particular page had been made from. Fishnet? The pages of a book or pamphlet whose ink had been effaced? The winding-sheet from some ancient skeleton? I thought how odd it was that each page, no matter how flawlessly white, no matter what its inscription or watermark, always harboured another text, another identity, beneath its surface, palimpsested and invisible, like a secret ink that can be seen only when rubbed with magic dust or exposed to flame. But what dust or flame, I wondered, might bring Sir Ambrose's message back to the surface, back to life?
I had tucked the cipher between the scantlings, beside another piece of paper, one also, it seemed, of inferior quality and inscribed with a worn goose quill. This was the letter from Alethea, dated five days ago, which Monk had retrieved from the General Letter Office. What secret message, I wondered, was occulted beneath its blotchy ink, behind the politely cryptic words that rose from the page in Lady Marchamont's old-fashioned scrawl?
I had read it through once again, feeling a turmoil in my belly and something insistent and unfamiliar nudging and squirming behind my breastbone.
My good Sir:
Please forgive the intrusion of another letter. I wonder if you might meet me in a week's time, on the 21st of July, at six o'clock in the evening? You may call for me in London, at Pulteney House, on the north side of Lincoln's Inn Fields. Suffice it to say, for the moment, that matters of some importance have arisen.
I shall look forward to your company. I fear the usual discretion must still apply.
Your most obliging servant,
Alethea