To either side, the thick green landscape passed unchanging, bedraggled under the rain, the only sound the muted thud of hooves on the wet turf as Sidney drew his horse alongside mine at the head of the party and allowed the palatine to fall behind, his head drooping to his chest, flanked by the two body servants who attended him, their horses carrying the vast panniers containing Laski's and Sidney's finery for the visit. I had only one leather bag with a few books and a couple of changes of clothes, which I kept with me, strapped to my own saddle. By the middle of the afternoon we had reached the royal forest of Shotover on the outskirts of Oxford. The road was poorly maintained where it passed through the forest, and we had to slow our pace so the horses would not stumble in the puddles and potholes.

"So, Bruno," Sidney said, keeping his voice low, when we were out of earshot of the palatine and his servants, "tell me more about this book of yours, that has brought you all the way from Paris."

"For the last century it was thought lost," I replied softly, "but I never believed that, and all through Europe I met book dealers and collectors who whispered rumours and half-remembered stories about its possible whereabouts. But it was not until I was living in Paris that I uncovered real proof that the book could be found."

In Paris, I told him, among the circle of Italian expatriates that gathered around the fringes of King Henri's court, I had met an aged Florentine gentleman named Pietro, who never tired of boasting to acquaintances that he was the great-great-nephew of the famous book dealer and biographer Vespasiano da Bisticci, maker of books for Cosimo de' Medici and cataloguer of the Vatican library. This Pietro, knowing of my interest in rare and esoteric works, recounted to me a story passed down to him by his grandfather, Vespasiano's nephew, who had been an apprentice to his uncle in the manuscript trade during the 1460s, in the last years of Cosimo's life. Vespasiano had assisted Cosimo in the collection of his magnificent library, making more than two hundred books at his commission and furnishing the copyists with classical texts, so that the book dealer became an intimate associate of the Medici circle, and in particular a friend of Marsilio Ficino, the great humanist philosopher and astrologer whom Cosimo had appointed head of his Florentine academy and official translator of Plato for the Medici library. As Pietro's grandfather, who was then the young apprentice, told it, one morning in 1463, the year before Cosimo died, Ficino came to visit Vespasiano at his shop, clearly in a state of some distress, clutching a package. Ficino had already begun work on the Plato manuscripts when he had received word from his patron that he must abandon them and turn his attention as a matter of urgency to the Hermetic writings, which had been brought out of Macedonia some three years earlier by one of the monks Cosimo employed to adventure overseas in search of books from the libraries of Byzantium, but which had yet to be examined. Perhaps Cosimo knew he was dying and wanted to read Hermes more than he wanted to read Plato in the last days of his life, I can only speculate. In any case, the story goes that Ficino told Vespasiano, ashen-faced and trembling, that he had read the fifteen books of the Hermetic manuscript and knew that he could not fulfil his commission. He would translate for Cosimo the first fourteen, but the final manuscript, he said, was too extraordinary, too momentous in its import, to put into the language of men hungry for power, for it revealed the greatest secret of Hermes Trismegistus, the lost wisdom of the Egyptians, a secret that could destroy the authority of the Christian church. This book would teach men nothing less than the secret of knowing the Divine Mind. It would teach men how to become like God.

Ficino had brought this devastating Greek manuscript to the shop with him, carefully wrapped in oilskins; here he handed it over to Vespasiano, exhorting him to keep it safe until such time as they could decide what should be done with it while Ficino would tell Cosimo that the fifteenth book had never been brought out of Byzantium with the original manuscripts. This was the plan, and the remaining books were duly translated; after Cosimo died the following year, Ficino and Vespasiano met to discuss the fate of the fifteenth book. Vespasiano saw the opportunity for profit and favoured selling it to one of the wealthy monastic libraries, where experienced scholars would know how to keep it safe from the eyes of those who might misinterpret or abuse the knowledge it contained; Ficino, on the other hand, had begun to regret his earlier delicacy and wondered whether it might not be better to translate the book after all, bringing its secrets into the light by revealing them first to the eminent thinkers of the Florentine Academy, the better to debate the impact of what was effectively the most blasphemous heretical philosophy ever to be uttered in Italy.

"So who won?" Sidney asked, forgetting to keep his voice down, his eyes gleaming through the stream of rainwater dripping from the peak of his cap.

"Neither," I replied bluntly. "When they came to take the manuscript from the archive, they made a terrible discovery. The book had been sold by mistake some months earlier with a bundle of other Greek manuscripts that had been ordered by an English collector."

"Who?" Sidney demanded.

"I don't know. Nor did Vespasiano." I lowered my eyes and we rode on in contemplative silence.

Here Pietro's story ended. His grandfather, he said, knew no other details, only that an English collector passing through Florence had taken the manuscript and that Vespasiano was never able to trace it, though he tried through all his contacts in Europe until the end of his long life, at the end of the last century. It was little enough to go on, I knew; there had been numerous English collectors of antiquities and rare books travelling through Italy in the past century, and there was no knowing whether the man who had acquired such a book by accident might have sold it or merely abandoned it to gather dust in some corner of a library, not realising what fortune had dropped into his hands.

"Then why do you believe it is in Oxford?" Sidney asked, after a while.

"Process of elimination. The English collectors travelling through Europe in the last century would have been educated men, probably wealthy, and I understand it is the custom of English gentlemen to leave books as a bequest to their universities, since precious few can afford to maintain private collections like your Doctor Dee. If the Hermes book ended up in England, it may well have found its way to Oxford or Cambridge. All I can do is look."

"And if you find it-?" Sidney began, but he was interrupted as his horse suddenly shied sideways with a sharp whinny; two figures had appeared without warning in the middle of the road. We pulled our horses up briskly, the palatine and his servants almost running into the back of us as we looked down at two ragged children, a girl about ten years old and a smaller boy, barefoot in the mud. The girl's right cheek was livid with a purple bruise. She held out her small hand, palm up, and addressed herself to Sidney in an imploring voice, though her stare was one of pure insolence.

"Alms, sir, for two poor orphans?"

Sidney shook his head silently, as if in sorrow at the state of the world, but reached at the same time for the purse at his belt and was drawing out a coin for the child when there came a sharp cry from behind us. I wheeled around just in time to see one of the palatine's servants dragged from his horse by a burly man who had emerged silently, along with two others, from among the shadows of the trees to either side. The palatine gave a little shriek, but gathered his wits remarkably quickly and spurred his horse into a gallop, crashing between Sidney and me and almost trampling the two children, who dived into the undergrowth just in time to watch him disappearing around the bend. I jumped from my horse, pulling Paolo's knife from my belt as I launched myself at the back of one of the assailants, who was swinging a stout wooden staff at the second servant to knock him out of his saddle. Sidney took a moment to react, then dismounted and drew his sword, making for the men who were now trying to cut the straps holding the packs to the horses.