He nodded and ran quickly to the right-hand staircase. Averting my eyes from Gabriel's body, I took the left.
I mounted slowly. My heart was thumping so hard it made my throat pulse, and white flashes danced before my eyes. I took off my heavy coat and laid it on the stairs. The cold chilled my bones but I had greater freedom of movement as I crept upwards.
The stairs led onto the narrow platform running round the interior. It was of iron mesh and, looking down, I could see far below the candles winking before the altar and the saints' shrines, the heap of stone and the great scarlet pool of Gabriel's blood. The platform was no more than three feet wide and only an iron rail separated me from the drop. Just ahead the mason's tools lay in an untidy heap beside the ropes, secured to the workmen's basket hanging out over the gap by rivets driven into the walls. I peered along the platform, cursing the poor light. All the windows were underneath the walkway and it was no more than twilit up there. I could not see far ahead, but there was someone ahead; there must be. I carefully manoeuvred my way along, bending to get under the ropes.
Just ahead the platform was level with the top of the rood screen. It ran from one side of the nave to the other, seven feet wide with, on the top, the statues at which I had previously peered from ground level. From there they had appeared quite small, but now, glancing at the dim figures through the gloom, I saw they were life-sized.
Cautiously, carefully gripping the rail, I moved down the platform past the screen. The rail creaked with every few steps and once I felt it wobble under my hand. I told myself that the mason and his men clattered along safely whenever they worked up here, but could not help wondering whether the blocks crashing over might have weakened it.
Across the church I made out Mark moving slowly along in parallel. He raised his sword and I waved my staff in acknowledgement. Between us, now, we must have the killer trapped. I gripped the staff hard. My legs had begun trembling and I cursed at them to be still.
I moved steadily on, staring ahead into the gloom. Nothing. No sound. As I approached the top of the church the walkway bent round in a half-circle, and a few moments later Mark and I were staring at each other, standing fifty feet apart at either end of the presbytery. And between us nothing, nobody. He looked at me incredulously.
'He came this way, I saw him,' he called.
'Then where is he? There's nobody this end of the church. You must have been mistaken, he must have headed down the other way, towards the door.' I stared back the way I had come, past the rood screen to where the end of the walkway was lost in the darkness.
'I'd swear on my life he came this way, I'd swear it.'
'All right.' I took a deep breath. 'Keep calm. If he's down the other end of the church we still have him. No one has gone down the stairs, we would have heard. We'll go back to the other end.'
'Perhaps we should go down. One of us could fetch help.'
'No, it's hard to keep an eye on both staircases at once, in a place this size he could slip away if he gets down.'
We took a parallel course once more, back the way we had come. My eyes were sore from peering intently ahead. As I passed the rood screen with its statues, something nagged at my mind. I was well past before it came to me: there had been the usual three statues: St John the Baptist, Our Lord and the Virgin. But there was a fourth as well.
Even as I paused and turned something whistled through the air and struck the wall beside me. A dagger clattered onto the walkway at my feet as I turned, realizing that what I had taken for the middle statue was in fact a living man in Benedictine habit. Even now a dim figure was clambering over the railing onto the walkway. I turned and ran towards him, but my foot caught in the mesh of the walkway and I fell forward onto the railing. For a second my head and shoulders hung out over the nave and I stared terrified over the drop, then I managed to haul myself upright. The figure had gone. I heard footsteps clattering down the stairs.