We made our way in silence. I was burning with anger; anger at Mark's thoughtlessness and insolence, but also at myself, for what he had said about my jealousy was true. To see him holding Alice, when she had shrunk from me, had burned me to the heart. I glanced sideways at him. First with Jerome, now with Alice. How could this obstinate, self-indulgent boy always leave me feeling in the wrong?

As we passed the church the monks were going in once more in double file. Simon was buried now in the monks' churchyard, but evidently there was to be a further service for him, though there had been none for Singleton. I reflected bitterly that Simon would have been grateful for a tenth of the attributes and opportunities God had lavished on Mark. The last of the brothers filed in, the door banged shut, and we walked on past the outhouses to the lay cemetery.

Mark stopped suddenly. 'Look there,' he said. 'That is strange.' He pointed to Singleton's grave, its brown earth standing out against the snow. The fresh snowfall had covered everything around with a further dusting, but not the grave.

We crossed to it and I exclaimed with disgust. The grave was covered with a viscous liquid, glittering in the weak sun. I bent down, touched it carefully and lifted my finger to my nose. Then I snorted angrily.

'Soap! Someone's coated the grave with soap. To prevent the grass growing. It has melted the snow.'

'But why?'

'Haven't you heard the story that grass will not grow on the graves of the sinful? There was a woman hanged for infanticide when I was a boy. Her husband's family would steal out and coat the grave with soap so nothing would grow, like this. It's a vicious piece of mischief.'

'Who has done it?'

'How should I know?' I snapped. 'God's passion, I'll have Abbot Fabian bring the lot of them out here to clean it under my supervision – no, under yours, it'll be a bigger humiliation to do it under you.' I turned away furiously.

We trudged on, traversing the graveyard and then the orchard, now almost a foot deep in snow. Watery sunlight was reflected from the stream and the ice-covered circle of the fish pond.

I pushed my way through the frozen rushes. The ice was thicker now, a light covering of snow round the edges. But by bending down and squinting hard I could still discern something gleaming faintly near the middle of the pond.

'Mark, see that pile of loose stones, under where the wall is patched. Fetch a big one and break the ice.'

He sighed, but at a stern look from me went off and fetched a great lump of limestone. I stood back as he raised the boulder above his head and flung it into the centre of the pond. There was a tremendous crash, satisfying somehow, though I flinched as a spout of water and shards of ice flew into the air. I left the water to settle, then carefully approached the edge, got down on hands and knees again and peered in. Disturbed fish milled about frantically.

'Now – yes, just there, do you see it? A gleam of yellow?'

'I think so,' Mark agreed. 'Yes, there's something. Shall I try fishing for it? If I take your staff and you hold my other arm, by stretching I might reach it.'

I shook my head. 'No. I want you to go in for it.'

His face fell. 'The water is near frozen.'

'Singleton's killer may have thrown his bloody clothes in there too. Go on, it can't be more than two or three feet deep. You'll live.'

For a moment I thought he would refuse, but he set his lips and bent to remove his coat, his overshoes and finally his boots. Those expensive leather shoes would be no better for a soaking. He stood a moment shivering on the bank, his solid bare legs and feet nearly as white as the snow. Then he took a deep breath and waded in, shouting aloud at the shock of the cold water.

I had expected it to reach his thighs, but he had taken no more than a couple of steps before, with a cry, he sank to his chest. Great bubbles of stinking gas belched up around him, smelling so vile I took an involuntary step back. He stood there gasping as the foul air dissipated.

'There's a foot of mud – ugh-' he gasped.

'Yes,' I said. 'Of course. The silt from the stream will fall to the bottom. Can you see anything? Can you reach?'

He gave me a withering look, then with a groan he bent down, his arm disappearing under the water. He scrabbled about. 'Yes – something – it's sharp-' his arm reappeared. He was holding a great sword, its handle gilded with gold. My heart leaped as he threw it on the bank.

'Well done!' I breathed. 'Now – again – is there anything more?'

He bent again, his whole shoulder disappearing under the surface and sending slow ripples towards the icy rim.

'Jesu, it's cold. Wait – yes – there is something – it's soft – cloth I think.'

'The killer's clothes!' I breathed.

He rose, pulling, and then overbalanced with a shout, falling right under the surface as another figure shot up out of the water. I gaped at the sight of a human form, dressed in a sodden robe. Its upper body seemed to hang in the air a moment, hair swirling round its head, then it splashed down into the reeds.

Mark's head rose again. He howled with shock and fear, flapping for the shore. Hauling himself onto the bank, he collapsed onto the snow, his yells turning to gasps and his eyes bulging, as mine were, at the sight of the figure in the reeds. A woman's body, grey and rotten and draped in the rags of a servant's dress. The eye sockets were empty; a lipless mouth was drawn back over grey clenched teeth. Rats-tails of hair dripped onto its face.

Mark got shakily to his feet. He crossed himself, over and over, praying. 'Deus salve nos, deus salve nos, mater Christi salve nos…'

'It's all right,' I said gently, all my anger gone. 'It's all right.' I put a hand on his shoulder; he was shaking like a leaf. 'She must have been lying under the silt. Gases built up and you disturbed them. You're safe, the poor creature can do us no harm.' But my own voice broke as I looked at the terrible thing lying there.

'Come, you'll catch an ague. Put on your boots.' He did so, the action seeming to calm him a little.

I saw that something else had risen to the surface and lay floating there; a large black piece of cloth, bloated with gas. I reached over with my staff, dreading a second body, but it was only an empty monk's habit. I hauled it in and set it on the bank. I could see dark patches that could have been the marks of congealed blood. I suddenly remembered the fat carp we had eaten on our first night and shuddered.

Mark was still staring at the body in horror. 'Who is it?' he stuttered.

I took a deep breath. 'My guess is those are the remains of Orphan Stonegarden.' I looked at the dreadful head, grey skin stretched over a skull. '"A sweet gentle face," Goodwife Stumpe said. "One of the prettiest I have ever seen." So this is what Simon Whelplay meant about warning a woman of danger. He knew.'

'So now we have three deaths.'

'I pray God it's the last.' I forced myself to pick up the monk's robe. I turned it over and paused at the sight of a little harp sewn into the fabric. I had seen it before; it was the sacrist's badge of office. My mouth fell open with amazement.

'It's Brother Gabriel's,' I gasped.