'Yes, I remember when I was at school how endless and frightening all the echoing corridors seemed if one was sent on an errand. All the doors one was not allowed to open.' I tried to be encouraging: 'But now I have a commission affording me every access. It's a place like every other, and we'll soon find our way around.' There was no reply and the sound of deep breathing told me Mark had fallen asleep. I smiled wryly, closed my eyes for a moment, and the next thing I knew there was a loud knock on the door and an exclamation from Mark as he was jolted awake. I got to my feet, surprisingly refreshed by my unintended sleep, my mind alert once more. I opened the door. Brother Guy stood outside, his candle casting the strangest shadows across his dark troubled face, his eyes serious.

'Are you ready to view the body, sir?'

'Ay, as ready as we'll ever be.' I reached for my coat.

In the infirmary hall the girl brought a lamp for Brother Guy. He donned a thick robe over his habit and led us along a dim, high-ceilinged corridor with vaulted ceilings.

'It is quickest to cross the cloister yard,' he said, opening a door into the cold air.

The yard, enclosed on three sides by the buildings where the monks lived and on the fourth by the church, made an unexpectedly pretty picture. Lights flickered at the many windows.

Surrounding the yard was the cloister walk, a covered area supported by elaborate arches. Long ago that would have been where the monks studied, in carrels lining the walk and open to cold and wind; but in these softer times it was a place for walking and talking. Against one pillar stood the lavatorium, an elaborate stone bowl used for washing hands, where a little fountain made a gentle tinkling sound. The soft glow from the stained-glass windows of the church made coloured patterns on the ground. I noticed strange little motes dancing in the light, and was puzzled for a moment before realizing it had started to snow again. The flags of the cloister yard were already speckled with white. Brother Guy led us across.

'You found the body, I believe?' I asked.

'Yes. Alice and I were up tending Brother August, who had a fever and was in much distress. I wanted to give him some warm milk and went to the kitchen to fetch some.'

'And that door is normally kept locked.'

'Of course. Otherwise the servants, and I regret also the monks, would help themselves to food whenever they wanted. I have a key because I often need things urgently.'

'This was at five o'clock?'

'The clock had struck a little before.'

'Had Matins begun?'

'No, Matins is sung late here. Usually towards six.'

'St Benedict's rule prescribes midnight.'

He smiled gently. 'St Benedict wrote his rule for Italians, sir, not people who have to live through English winters. The office is sung and God hears it. We cut through the chapter house now.'

He opened another door and we found ourselves in a large chamber, its walls richly painted with biblical scenes. Stools and cushioned chairs were dotted around, and there was a long table before a roaring fire. The room was warm and musty with body odour. About twenty monks sat around; some were talking, some reading, and half a dozen were playing cards at a table. Each monk had a pretty little crystal glass by his elbow, filled with green liquid from a large bottle of French liqueur that stood on the card-players' table. I looked round for the Carthusian, but there was no white habit among the black; the straggle-haired sodomite Brother Gabriel and Mortimus the sharp-eyed bursar were also absent.

A thin-faced young monk with a wispy beard had just lost a game, judging by his annoyed expression.

'That's a shilling you owe us, Brother,' a tall, cadaverous monk said cheerfully.

'You'll have to wait. I will need an advance from the chamberlain.'

'No more advances, Brother Athelstan!' A plump old brother sitting nearby, his face disfigured by a warty growth on one cheek, wagged a finger at him. 'Brother Edwig says you've had so many advances you're getting your wages before you've earned them-' He broke off, and the monks hastily rose to their feet and bowed to me. One, a young fellow so obese even his shaven head was lined and puckered with fat, knocked his glass to the floor.

'Septimus, you dolt!' His neighbour prodded him sharply with his elbow, and he stared round with the vague glance of the simple-minded. The monk with the disfigured face stepped forward, bowing again obsequiously.

'I am Brother Jude, sir, the pittancer.'

'Master Matthew Shardlake, the king's commissioner. I see you are enjoying a convivial evening.'

'A little relaxation before Vespers. Would you care for some of this fine liqueur, Commissioner? It is from one of our French sister houses.'

I shook my head. 'I still have work to do,' I said severely. 'In the earlier days of your order, the day's end would have been taken up with the Great Silence.'

Brother Jude hesitated. 'That was long ago, sir, in the days before the Great Pestilence. Since then the world has fallen further towards its end.'

'I think the English world does very well under King Henry.'

'No, no-' he said hastily. 'I did not mean-'

The tall thin monk from the card table joined us. 'Forgive Brother Jude, sir, he speaks without thinking. I am Brother Hugh, the chamberlain. We know we need correction, Commissioner, and we welcome it.' He glared at his colleague.

'Good. That will make my work easier. Come, Brother Guy. We have a corpse to inspect.'

The fat young monk stepped forward hesitantly. 'Forgive me slipping, good sire. My leg pains me, I have an ulcer.' He gave us a woebegone look. Brother Guy put a hand on his shoulder.

'If you would follow my diet, Septimus, your poor legs would not have to bear such weight. No wonder they protest.'

'I am weak flesh, Brother, I need my meat.'

'Sometimes I think it a pity the Lateran Council ever lifted the prohibition on meat. Now excuse us, Septimus, we are on our way to the crypt. You will be pleased to hear Commissioner Singleton may be laid to rest soon.'

'Thanks be to God. I am afraid to go near the cemetery. An unburied body, an unshriven man-'

'Yes, yes. Go now, it is almost time for Vespers.' Brother Guy gently moved him aside and led us through another door, out into the night again. An expanse of flat ground lay ahead, dotted with headstones. Ghostly white shapes stood out here and there, which I recognized as family crypts. Brother Guy raised the hood of his habit against the snow, which was coming down thickly now.

'You must forgive Brother Septimus,' he said. 'He is a poor silly creature.'

'No wonder his leg gives trouble,' Mark observed. 'Carrying all that weight.'

'The monks stand for hours at a time in a cold church every day, Master Mark, a good covering of fat is not unhealthy. But the standing brings on varicose ulcers. It is not so easy a life. And poor Septimus has not the wit to cease from gorging.'

I shivered. 'This is not the weather to stand talking.'

Holding his lamp high, Brother Guy led us between the headstones. I asked him whether, when he came to the kitchen that morning, the door had been locked.

'Yes,' he replied. 'I went in through the door from the cloister yard, which is always locked at night, then up the short passage leading to the kitchen. The kitchen itself is not locked because the only way is via the passage. I opened the door and at once I slipped in something and almost went over. I put my lamp down, then saw that headless body.'

'Dr Goodhaps said he slipped too. So the blood was liquid?'

The infirmarian considered. 'Yes, it had not started to congeal.'

'So the deed had not been done long?'