After a while Mark reappeared. I was relieved to note, as he opened the door, that the sawing had stopped.

'I have signed for the account books, sir. Eighteen great tomes. There was much grumbling from the bursar's men about how this will disrupt their work.'

'A pox on their work. Did you lock our room behind you?'

'Yes, sir.'

'Did you happen to notice whether any of the books had a blue cover?'

'They were all brown.'

I nodded. 'I think I know why Brother Edwig has been giving young Athelstan a hard time. There was something he did not tell us earlier. We will have another talk with our bursar, this could be important-' I broke off as Brother Guy came in. His face was drawn and pale. Under his arm was a stained apron which he threw into a basket in the corner.

'Commissioner, might we have a private word?'

'Of course.'

I rose and followed him. I feared he would take me to poor Whelplay's body, but to my relief he led me outside. The sun was beginning to set, casting a pink glow over the white herb garden. Brother Guy picked his way among the plants until he came to a large, snow-covered bush.

'I know now what killed poor Simon, and it was not possession by a demon. I also noticed him twisting his body over and waving his hands. But it was nothing to do with you. The spasms are characteristic. And the loss of voice, the visions.'

'Characteristic of what?'

'Poison from the berries of this bush.' He shook the branches, to which a few black dead leaves still clung. 'Belladonna. The deadly nightshade, as it is called in this country.'

'He was poisoned?'

'Belladonna has a faint but distinctive smell. I have worked with it for years, I know it. It was in poor Simon's guts. And in the dregs of the cup of warm mead by his bed.'

'How was it done? When?'

'This morning, without doubt. The onset of symptoms is rapid. I blame myself, if only Alice or I had stayed with him all the time-' He passed a hand over his brow.

'You could not have known this would happen. Who else spent time alone with him?'

'Brother Gabriel visited him last night late, after you retired, and again this morning. He was most upset, I gave him permission to pray over the boy. And the abbot and bursar came to see him later.'

'Yes. I knew they were coming.'

'And also this morning, when I went in to check on him, I found Prior Mortimus there.'

'The prior?'

'He was standing by the bed, looking down at him, a worried look on his face. I thought he was worried about the consequences of his harsh treatment.' He set his lips. 'Belladonna juice is sweet-tasting, the smell too faint to be noticed in mead.'

'It is used as a remedy for some ailments, is it not?'

'In small doses it relieves constipation, and has other uses. There is some in my infirmary, I often prescribe it. Many of the monks will have some. Its properties are well known.'

I thought a moment. 'Last night Simon began to tell me something. He said Commissioner Singleton's death was not the first. I intended to question him again today when he woke.' I gave him a sharp look. 'Did you or Alice tell anyone what he had said?'

'I did not, and nor would Alice. But he might have rambled deliriously to his other visitors.'

'One of whom decided his mouth must be stopped.'

He bit his lip and nodded heavily.

'Poor child,' I said. 'And all I could think of was that he was mocking me.'

'Things are seldom what they seem.'

'Here least of all. Tell me, Brother, why have you told me this rather than going straight to the abbot?'

He gave me a bleak look. 'Because the abbot was among his visitors. You have authority, Master Shardlake, and I believe you seek the truth, however much I suspect we might disagree on matters of religion.'

I nodded. 'For the moment I instruct you to keep secret what you have told me. I must think carefully how to proceed.' I looked at Brother Guy to see how he would take orders from me, but he only nodded wearily. He looked down at my mud-caked leg.

'Have you had an accident?' he asked.

'I fell in the bog. I managed to get myself out.'

'The ground is very unsafe out there.'

'I think there is no safe ground under my feet anywhere here. Come inside, or we'll catch an ague.' I led the way indoors. 'Strange that my misplaced fear he was mocking me should lead to this discovery.'

'At least now Prior Mortimus cannot say that Simon is surely in hell.'

'Yes. I think that may disappoint him.' Unless he is the killer, I thought, in which case he knows already. I gritted my teeth. If I had not allowed Alice and Brother Guy to dissuade me from talking to Simon last night, not only might I have had his full story, not only might I have been led to the killer, but Simon would still be alive. Now I had two murders to investigate. And if what the poor novice had muttered in his delirium about Singleton not being the first was true, then there were three.

I had hoped to go into Scarnsea that afternoon, but it was now too late. In the last glow of the sunset I trudged again through the precinct to the abbot's house, to talk to Goodhaps. The old cleric was again bibbing alone in his room. I did not tell him that Novice Whelplay had been murdered, only that he had been very ill. Goodhaps seemed uninterested. I asked him what he knew of the account book Singleton had been studying just before his death. Singleton, he said, had told him only that he had prised a new book out of the counting house, which he hoped would be useful. The old man muttered in a surly tone that Robin Singleton kept much to himself, using him only to burrow in books. I left him to his wine.

A cold, keening wind had risen, cutting through me like a blade as I made my way back to the infirmary. As those loud bells pealed out again for Vespers I could not help reflecting that anyone who might have information was at risk: old Goodhaps, or Mark, or me. Whelplay's killing had been carried out with a cold and ruthless hand, and might have escaped detection had I not put Brother Guy in mind of belladonna by mentioning Simon's strange postures and gestures. We might be dealing with a fanatic, but not someone ruled by impulse. What if he was planning to put poison in my dinner plate, or sought to make a gap between my head and shoulders such as he had with Singleton's? I shivered and pulled my coat tighter around my neck.

Books were stacked on the floor of our room. Mark sat staring into the fire. He had not yet lit the candles, but the firelight cast a flickering glow over his troubled face. I sat opposite him; the chance to rest my poor bones by a warm fire was welcome.

'Mark,' I said, 'we have a new mystery.' I told him what Brother Guy had said. 'I have spent my life deciphering secrets, but here they seem to multiply and grow more terrible.' I passed a hand over my brow. 'And I blame myself for that boy's death. If only I had insisted, last night, in pressing him. And there in the infirmary, when he bent his poor body and waved his arms, all I could think of was that he might be mocking me.' I stared bleakly before me, momentarily overcome with guilt.

'You were not to know what had happened, sir,' Mark said hesitantly.

'I was tired, I allowed myself to be pressed to leave him. Lord Cromwell said in London that time was of the essence. Now here we are four days later with no answers and another death.'

Mark stood up and lit candles from the fire. I felt suddenly angry with myself; I should be encouraging him, not giving in to despair, but the novice's death had momentarily overwhelmed me. I hoped his soul had found rest with God; I would have prayed for it had I believed prayers for the dead made any difference.