'You may consult with the lapicide or stonemason who carved the stone,' he suggested. 'Ordinarily they inscribe their name or a coat of arms on the rear of the slab.'

But I was loath to creep back to Cobb's gravestone in broad daylight-almost as loath as I was to enter the noise and dust of a stonemason's yard in both the heat of the day and the aftermath of Biddulph's rumbullion. And so I returned to Nonsuch House, wondering what I should make of the things I had learned; if in fact I had learned anything at all.

For the remainder of that day I went about my usual ceremonies among my shelves and customers. Ah, the pleasant balm of routine, what Horace calls laborum dulce lenimen, the 'sweet solace of my toils'. Afterwards I ate a dinner cooked by Margaret, drank two cups of wine and smoked a pipe of tobacco, then retired to bed at ten o'clock, my usual hour, with Wolfram's Parzival-I had decided against Don Quixote that night-propped on my belly. I must have fallen asleep soon after the watchman announced eleven o'clock.

I have never been a good sleeper. As a child I was a notorious sleepwalker. My strange trances and midnight perambulations regularly alarmed my parents, our neighbours, and finally Mr. Smallpace, who once led me back to Nonsuch House, barefoot and confused, after I wandered as far as the south gate of the bridge. As I grew older, this nocturnal restlessness translated itself into bouts of insomnia that plague me to this day. I will lie awake for hours on end, incessantly checking my watch, plumping and punching my pillow, thrashing and turning on my mattress as if wrestling a foe, before sleep at last whelms over me only to subside a minute later when I am disturbed by the slightest noise or provoked by the jagged shard of an unremembered dream. Over the years I have sought out various apothecaries who have prescribed all manner of remedies for the condition. I have drunk by the pint-pot foul-smelling syrups made from maidenhair and the seeds of poppies (a flower that Ovid tells us blooms beside the Cave of Sleep), or rubbed on to my temples an hour before retiring, as per instructions, other concoctions mixed from lettuce juice, oil of roses and who knows what else. But none of these expensive elixirs has ever managed to hasten my slumbers by so much as a single minute.

To make matters worse, Nonsuch House is an unfamiliar and even frightening place after dark, especially so, it seemed, after Arabella's death-a vast echo-chamber where floor timbers creaked and groaned, shutters rattled, the chimney keened, the eaves gargled, beetles tapped, rats squeaked and scurried, and the elm pipes shuddered and moaned behind the walls as the water inside them either froze or thawed. I think of myself as a rational man, but in the months after Arabella's death I used to jolt awake several times each night, stark with terror, then hunch beneath the counterpane like a horror-struck child, listening to a platoon of ghosts and demons whispering my name as they went about their stealthy work in my closets and corridors.

Tonight I was awakened with a start by one of these noises. Jerking upright in the darkness, I fumbled on the bedside table for the firelock. I had considered sleeping with it under my pillow, as I believe people are said to do for fear of housebreakers, but had visions of it discharging itself as I rolled over in my sleep, and anyway it had been far too big and uncomfortable to fit under my tiny goose-down pillow. So I had placed it on the table instead, charged with a ball and powder, though with the barrel pointing away from the head of the bed. The rest of the ammunition was in the drawer, in a bandolier that the one-legged veteran had sold me along with the firelock: thirty balls of lead that looked curiously harmless, like the petrified droppings of a small rodent.

I found the pistol only after a few seconds of frantic scrabbling, then closed my fingers over the stock and held my breath, listening for the intrusive noise. It had been, I thought, some sort of faint rattling or jingling, like a pair of spurs. But all was silent now. The noise had been a dream, I told myself. Or the watchman with his bell.

Ka-chink, ka-chink, ka-chink-a…

I had just fallen asleep when I caught it again, more clearly this time, an unfamiliar sound not in the building's usual repertoire: a faint but insistent jingling, like a small dinner-bell or a set of keys on a chatelaine. Or perhaps like a set of traces, except that it was hours past curfew, the gates would be closed, and no horse-and-carriage was likely to be passing along the carriageway.

I pushed myself upright again, left hand grappling for the pistol. I struck a taper and squinted at my watch, which I also had to fumble for on the bedside table. Past two o'clock. Abruptly the noise stopped, as if the perpetrator had caught himself and swiftly muffled it. I swung my legs over the edge of the bed, imagining the instigator hunched against a wall somewhere, breath held and ears trained.

Ka-chink-ka-chink-ka-CHINK!

The noise had grown louder and more insistent by the time I stole along the corridor and then, drawing a deep breath, down the first few steps. I had trouble with my footing in the dark but managed to avoid the third tread from the top, which squeaked, and the fifth from the top, whose riser-in order to trip unwary housebreakers-was four inches higher than the rest. I had no wish to rouse Monk, who would have been frightened to death by the sight of me slinking about the house, pistol in hand. Nor did I wish to alert the intruder who-I was sure of it now-was either inside the shop or else attempting to prise his way through the outer door: for the sound had been caused, I realised, by a ring of picklocks.

Ka-CHINK-a…

My nape prickled with fear. Drawing a shuddering breath I tightened my grip on the weapon and searched with a bare foot for the next tread. The jingling had ceased, but now I heard the catch click and then caught the slow creak of my new hinges as the green door was opened inchmeal. I froze, club foot suspended in mid-air. The floor timbers complained gently as the intruder stole across the shop. I licked my lips and felt blindly for another step.

What happened next was inevitable, I suppose. The steps of the turnpike staircase are steep, shallow and worn, their risers of irregular height; and of course I am a cripple and half blind without my spectacles, which I had left behind in my bedchamber. So when I reached for another step, my club foot skittered over the edge of the next tread and I pitched forward with a yelp to the landing. Worse, I lost my grip on the pistol as I flailed through the darkness. It clattered noisily down the steps ahead of me.

I caught my breath and held it. Dead silence followed. I lay on the landing for a few seconds before cautiously unfolding myself and rising to a crouch. So silent had everything fallen that for a second I almost thought I had been mistaken, that all had been a dream, or the sound of the wind, or the building lurching and creaking with the tide. But then I heard the unmistakable tread of feet and, seconds later, whispering voices.

I felt my body tense, bracing itself to lunge. I might still reach the pistol. But there were at least two intruders, while even if I reached the weapon first I had only one shot. So I remained in a crouch on the landing, too frightened even to breathe.

A few horrible seconds passed before I heard the sharp gasp of a taper. Then a light welled upwards and shadows pivoted across the wall. I sprang into motion, lurching crabwise along the narrow landing, fumbling for the steps above me. But it was too late. Already a pair of boots was squeaking on the treads, only a few feet below now. I heard the soft whoosh of the burning torch, then a loud scrape as the pistol was recovered. Another few seconds and they would reach me.