Their desire for reformation was understandable enough, I supposed. What did the Rosicrucian see as they gazed back over the last hundred years of European history but slaughter-benches drenched in Protestant blood? There was the massacre of Huguenots in Paris on the Feast of St. Bartholomew and the bonfires at Smithfield and Oxford during the reign of Queen Mary. There were the horrors of the Spanish Inquisition and the Holy Office, along with the wars of the Spaniards in the Low Countries, where Sir Philip Sidney lost his life. There were the Lutheran clergymen expelled from Styria and the bonfire of 10,000 Protestant books in the city of Graz, from which Kepler was banished. There was Copernicus, bullied and silenced, and Galileo, summoned to Rome in 1616 for examination before Robert Bellarmine, one of the cardinals of the Inquisition who had burned the Hermetic philosopher Giordano Bruno in the Campo de' Fiore. There was Tommaso Campanella tortured and imprisoned in Naples. There was William the Silent murdered by Spanish agents and Henry IV stabbed by Ravaillac on the Pont Neuf.

In the end, though, the Rosicrucians themselves became a part of this tragic litany. They discovered neither the philosopher's stone nor their cherished Golden Age, because in 1620 King Frederick and the Bohemian Protestants were crushed by the armies of the Catholic League. Undoubtedly most Brothers of the Rose Cross were superstitious charlatans and foolish idealists, but I had felt a sorrow for these men who had wished to ward off with their books and chemicals and feeble magic spells what they saw as the evils of the Counter-Reformation, of Spain and the Habsburgs, only to be swallowed up themselves in the horrors of the Thirty Years War.

But this morning as the coach jolted past Chancery Lane something else about the Rosicrucian Brethren had struck me. I realised that their manifestos had appeared in Prague at roughly the same time that Raleigh's fleet-financed by another band of zealous Protestants-was setting sail for Guiana. Indeed, the most famous of the Rosicrucian tracts, The Chemical Wedding of Christian Rosencreutz, a copy of which I discovered on my shelves, was published in Strasbourg in 1616, the same year that Raleigh was released from his cell in the Bloody Tower. So I wondered again if Sir Ambrose with his Hermetic text was some sort of link between these two doomed ventures, the first with Raleigh in Guiana, the second with Frederick in Bohemia. I had no idea; but the other day as I glanced through my copy of The Chemical Wedding I noticed something else about the text, something even more dramatic than its date, for engraved both in its margins and on the title page were tiny Mercury symbols, exact duplicates of these figures scribbled on the walls of London.

Then the coach had reached Bishopsgate, where the gates were scraped open to admit a flock of geese being driven to market for slaughter. I had pulled the window-curtain and closed my eyes, but as the coach creaked about me I found myself thinking of the dozens of alchemical works at Pontifex Hall, along with its well-stocked laboratory, and I wondered if Alethea's father, a devout Protestant, had been a Rosicrucian too. But at that point my thoughts had been interrupted as the cackling of the jubilant geese fell about my ears-the riotous clamour of creatures oblivious to the fate that lay only a few minutes away.

'Hungry, sir?'

'Mmmn…?' The voice had startled me awake, and for a few seconds I was too disoriented to move or speak.

'Shall we stop for a meal, sir?'

I pushed myself upright and peered through the window flap, confused and blinking, feeling the dislocation I always experience when I abandon the city for the country. A flat landscape was slowly reeling past, its fields and wood-lined droves half underwater. Rain was still falling in curtains, drumming across the leather rooftop.

'How long before Cambridge?'

'An hour,' replied Crump.

'No.' I fell back into the seat. 'Carry on.'

In fact it took two more hours to reach Cambridge, but by that time the rain had stopped and the sky at last blew clear. An impressive sunset one hour earlier had turned to soft pink a herd of sheep straggling across the flat chalklands. When I thrust my head through the window I had felt a damp wind pluck at my hair and noticed a mud-speckled coach-and-four trailing us at a distance; then a horseman on a blue roan trailing the coach. But I thought little of them at the time. The road as we neared Cambridge was thick with all sorts of coaches, riders on horseback, stage-wagons bound for London or Colchester. I leaned back in the seat and closed my eyes.

The plan had been to stay the night in Cambridge and set out at first light for Wembish Park. To that end, Crump proposed a posting-inn called the Bookbinder's Arms, which he claimed stood by Magdalene College, overlooking the river. I readily consented. So far Crump had proved himself a remarkably capable guide.

But it was at this point that our journey suffered a bewildering setback. It might have been the growing darkness, or Crump's exhaustion, or the crowded streets with their rows of overhanging buildings. Or it might have been the reluctance of the post-horses, who were refusing each gate or unlighted bystreet and worrying at their snaffles. Whatever the reason, however, the aplomb with which Crump had found our way through Epping Forest and the fifty-odd storm-racked miles now seemed to desert him. For the next three-quarters of an hour we wound through narrow streets barely an arm's span wide, passing college after college, post-inn after post-inn, circling back upon ourselves, squinting and craning our necks, blundering across causeways and bridges only to be brought up short by ditches or cul-de-sacs, all without coming upon either Magdalene College or the Bookbinder's Arms. So at last Crump invited me to share the coach-box with him: I would watch for the inn, he said, while he concentrated on the business of driving.

There was barely room enough for two in the seat, but for a long while we rode in this fashion, our feet side by side on the footboard, our shoulders rubbing together. He had fallen silent and kept his eyes trained on the street ahead, while I twisted back and forth, looking out for signboards and, at the same time, studying him more closely. He was an ox of a man with pale eyes, blond hair and a drinker's nose that was pitted like a Seville orange. I had met him before-I was certain of that by now-but could not remember where. He might have been one of the labourers at Pontifex Hall, I thought, or one of the patrons blowing on his coffee in the Golden Horn.

For an instant a memory seemed to shimmer and rise on the edge of the horizon, but then we struck a bump in the road and I had to grasp the edge of the seat to stay aboard. As I did so, I felt a sudden pressure on my hip and, looking down, saw the butt of a pistol in Crump's waistband. I raised my eyes to his face and was alarmed to see something new-a look of worry, maybe even fear-inscribed across its weathered furrows.

'Shall we stop here?' I asked, pointing to an approaching inn whose unscrubbed stable-yard could be smelled even from this distance. We had passed its signboard twice already. 'This one looks adequate. What does it matter? They're all the same, these inns.'

'Keep your mouth shut and your eyes open,' he growled, working his mandibles fiercely and giving the reins a hard shake. 'You might miss something.'

The St. George & Dragon slipped past, as did the Shepherd's Crook, the Shoulder of Mutton, the Faggot of Rushes, the Merrie Lion, the Leathern Bottle, the Sow & Pigs, plus at least a half-dozen other inns and taverns, all of which Crump refused to consider. I decided I would jump down on to the street and make my own way-with or without Crump-to one of the other inns. But just as I rose from the seat and balanced myself on the footboard, steadying myself to leap over the wheel and on to the bridge, I suddenly caught sight of the Bookbinder's Arms, a pale hulk with flickering windows and a steep roof that rose against the sky like a ziggurat. It stood directly across the river from us, on the opposite side of a narrow bridge on to which Crump was guiding the horses.