'The springs rise over there,' Alethea said, 'to our left. Just past the orangery.'

I turned my attention from the hedge. The two of us were standing to the west of Pontifex Hall, a few yards beyond the reach of its great quadrangular shadow, which stretched towards us across the sward. Alethea was pointing past a shallow pit, clogged with debris, above which a few miserable spars rose like ancient, idolatrous forms. Heaped about them were shards of old masonry. Beyond, on higher ground, a scattering of rocks had been arranged in broken geometric patterns.

'You can still see the remains of the dip-well.'

She nodded in the direction of the concentric rings. Once again her hand had grasped my forearm, this time in a gesture of intimacy. In the fresh light her soiled gown now proved not black after all but a mallard green. The hooded mantle, still draped over her shoulders despite the heat, looked to be embroidered with tiny faded flowers.

'The springs pour out of the rocks,' she continued, 'and into the dip-well and cress-pond, both devised by my father. From there the water disappears down a drain and runs towards the wings of the hall in a network of channels. The water was tamed and used in fountains and waterfalls. Even a giant waterwheel. It stood over there,' she said, turning to point vaguely to the south of the hall.

'All built by Sir Ambrose.'

'Of course. He was granted a number of patents for water pumps and windmills.'

She fell silent. At times this morning she seemed distracted, absorbed in some private, melancholy reverie that manifested itself in silence and oblique, unfathomable glances. We skirted the devastated orangery and now stood at the edge of the stone-lined cress-pond. It was infested with duckweed, and even at this hour its surface was thick with clouds of gnats.

When her silence promised to endure, I turned to look back at the gaunt hulk of Pontifex Hall, trying unsuccessfully to imagine the fountains and waterworks in place of the weed-choked sward and overgrown hedge now confronting us. A single magpie was swaggering across it, coming in our direction. A bad omen, my mother would have said: one for sorrow, two for joy. Instinctively I looked for a second bird but, shading my eyes, saw only the leavings of the workmen hired to restore the house, a careless litter of chisels, brick hammers, bullnose planes, handsaws. Several tarpaulins, their corners pinned by bricks, shrouded thick sheets of marble. For the fireplaces, Alethea had explained. A half-finished wooden scaffold clambered awkwardly up the scarred wall of the north wing. Beneath it lounged one of the plasterers, smoking a tobacco-pipe and throwing us the occasional glance.

By now an hour had passed since I fled the chamber with the torn page tucked in my pocket, next to my original summons. On my second attempt I had negotiated the passages unerringly; the door that originally impeded my progress had proved not to be locked, but merely stiff, and I found my way downstairs in a few minutes. It was as if the alien leaf had been some sort of key or passport-a golden skein-without which I was doomed to endless wanderings above stairs. Phineas had been awaiting my arrival in the breakfast parlour. Lady Marchamont, he explained, had already eaten and was outside in the park. If I would be so good as to take a seat, then Miss Bridget would be pleased to serve me. Then Lady Marchamont was most anxious that I should join her for a walk.

The paper was crackling softly in my pocket as the two of us returned to the house, walking side by side and passing the dozens of stunted, limbless trunks that rose through the overgrowth of what was once an orchard. I had already decided that it was a cipher, some kind of encrypted message. But encrypted by whom?

The sound of the shears grew louder as we approached the ravaged hedge, and the gardener's disembodied head bobbed and floated along the irregular green parapet. A complex pattern was defining itself as more and more branches fell away. It seemed not just one hedge, but rather a dozen, all interconnected. The lines of the plantation appeared to imitate the angles of bastions, half-moons, scarps, counter-scarps, like the model of a fortress-a series of concentric rings like those of the drip-well. What was the purpose? A puzzle maze? I was shading my eyes, studying the row of unpruned hornbeam; the dark patches of yew, the newly gravelled pathway imperfectly penetrating the wall.

Yes, a hedge-maze: an 'infernal garden' like those I had read about at the castles in Heidelberg and Prague. Through the arched entrance I could see the intricate windings beginning to take shape. The plan, I supposed, had been destroyed or lost, so that now the fractured outlines of the garden formed an impossible, patternless labyrinth. The gardener had bent his head and the shears were snapping furiously. Did a premonition nudge me as we passed, or is it merely the warping eyepiece of memory-the memory of those events that were so shortly to follow-that now gives horrible resonance to the sight of that overgrown maze and the gardener with his murderous blades?

'The pipes have become blocked.' Roused from her reverie, Alethea was continuing her account. 'They were made of the hollowed trunks of elm trees, which underground have a life expectancy of only twenty-five, perhaps thirty, years. After that, they tend to collapse, or clog or leak. Then the water flows everywhere.' She pulled up short and gazed across at the scaffolded wing of Pontifex Hall. 'The foundations of the house are being undermined, you see. Water is pooling underneath, more of it every day. I am told that in a few months the entire house might collapse.'

'Collapse?' I had turned from the hedge-maze and was shielding my eyes as I peered up at the tragic spectacle of Pontifex Hall. I thought suddenly of the sounds last night in the crypt, the steady rush of unseen waters. 'Can the waters not be dammed at the source? Or conducted away?'

'The sources are too numerous for a dam. The springs rise at five or six points at least. Some of them haven't even been found. The whole building is being undermined by an underground river. So, yes, the water must be conducted away. I have an engineer in London working on plans for a new set of pipes.' She gave an exhausted sigh, then tugged my arm as she had at the door to the muniment room. 'Come.'

As we walked through the grounds Alethea described something more of the house's history. It was a replacement, she said, for one built in the time of Queen Elizabeth, which in turn was a replacement for Pontifex Abbey, an ancient foundation confiscated by Henry VIII from its little band of Carmelite friars after the Act of Dissolution in 1536. The history of the house seemed to be one of growth and destruction, of one building rising from the ashes-sometimes literally-of another, a cycle of oblivion and renewal. She indicated where the vineyard and herb garden of the dissolved abbey had extended; where its confiscated library had stood; where cupolas, bell-towers and turrets once reared high above surrounding crofts and wastes. All were now long vanished except for the odd earthwork or cairn of shattered masonry-so many scars and old bones. I was reminded, suddenly, of what she had said earlier about civilisation being founded by acts of desecration. But how in that case, I wondered, did one tell the difference between them, between acts of civilisation and those of barbarism?

'The Elizabethan house burned down some fifty years ago, killing its inhabitants, an ancient family named de Courtenay. Quite impoverished, I believe. A year after the fire, my father purchased the freehold from the family's even more impoverished heir, a cheesemonger in Dorchester. Over the course of the next five or so years he raised the current house. He designed it himself, you understand. Every last detail of its construction, both inside and out.'