'And everything comes from the four elements. Earth, air, fire and water. Any new material that appears, like that strange stuff, can be broken down into those essential elements and reconfigured.'

He smiled. 'There is nothing truly new in the world. No new elements, at least. But a good alchemist may, for example, discover by careful observation how to melt down ores in the furnace in such a way as to produce better iron, as they are doing in the Weald now.'

'Or how to make a finer form of pewter,' I said, remembering Goodwife Gristwood's story of Sepultus's failed experiments.

'Exactly. It is usually a matter of separating out some impurity of an earthy nature.' He smiled. 'I am with those thinkers who consider God means us to uncover the secrets of the earth by the slow, sure path of observation rather than mystical formulae in ancient books. Even if they do come up with some strange notions, like the man in Poland who says the earth goes round the sun.'

'Yes.' Something had stirred a memory. 'A furnace, you said. You remind me that metals are forged in furnaces. So alchemists must often work with founders, as they all have furnaces.'

'Of course,' Guy agreed. 'I make do with a fire here to distil my herbs, but to melt ores and metals a furnace would be needed.' He frowned. 'This is a strange discussion, Matthew. What has it to do with this – ' he glanced at Barak – 'this case of yours?'

'I'm not sure.' I frowned in thought. 'A founder would also be needed to make, say, a large metal tank with a pump and pipes.'

'Yes. Alchemists often have arrangements with the Lothbury founders to assist them. It has to be someone they trust, of course, if they're to share their secrets.'

'Guy,' I said excitedly, 'do you remember that young founder I met last week? Would he know who might work with alchemists up there? And perhaps one who works with the City on the water conduits, works with pumps and valves?'

He hesitated. 'Perhaps. That would be a specialized trade. But Matthew, if this is a dangerous matter, I would not involve him.'

'Lord Cromwell may command it,' Barak said.

Guy turned to him. 'He may command what he wishes,' he said imperturbably.

Barak glared. 'Yes, my Spanish friend, he may.'

'God's death, Barak, be quiet,' I said angrily. 'I understand, Guy. I can find what I need as easily from the City records, see whom they employ on the conduits.'

Guy nodded. 'I would prefer that.' He turned back to Barak. 'And by the way, sir, I am not Spanish. I come from Granada, which was conquered by Spain fifty years ago. My parents were Moslems who were expelled from Spain by Ferdinand and Isabella. Along with the Jews – yours is a Jewish name, I think.'

Barak reddened. 'I am English, apothecary.'

'Are you now?' He raised an eyebrow. 'Ah well. Thank you for your understanding, Matthew. I wish you safe in your quest.' He shook my hand, then looked at me wryly. 'Your eyes are alight, Matthew, alight with the prospect of progress in your chase. May I keep those books, by the way? I should be interested to look through them.'

'Please do.'

'If you want to talk more, I am here.' He gave Barak a cold look. 'So long as foreigners are allowed to remain.'

OUTSIDE I TURNED angrily on Barak. 'Well done,' I said. 'Your manners really helped our enquiries.'

He shrugged. 'Insolent old Moor. God's teeth, he's an ugly creature.'

'And you,' I snapped, 'you are what you call everyone else – an arsehole.'

Barak only grinned.

'Since you probably lost us Guy's help in finding the founder, you can go up to the Guildhall and ask for details of all the founders they employ on the conduits. I am going to Wolf's Lane to ask Goodwife Gristwood a few more questions. If Michael and Sepultus were visiting the founders, she must have known about it.'

'I thought we were going across to Southwark to find the whore.'

'I'll meet you at the Steelyard steps in an hour and a half. Who knows, I may even have time to grab a pie from a stall.' I wiped sweat from my brow, the heat of the afternoon was punishing. Barak hesitated and I wondered if he were going to argue: I felt so angry I would almost have welcomed it. But he only smiled, mounted his black mare and cantered away.

AS I RODE THROUGH the narrow streets to Queenhithe my anger ebbed. I found myself once more watching fearfully for dangerous movements in the shadows. The streets were empty, people indoors avoiding the heat if they could. I felt my cheek prickle with sunburn and pulled my cap lower. I jumped as a rat scurried from a doorway and ran down the street, hugging the wall.

The Gristwoods' house was unchanged, the split and broken front door still in place. I knocked, the sound echoing within. Jane Gristwood herself opened the door. She wore the same white coif and grey dress and there was a new unkemptness about her appearance; I saw food stains on the dress. She stared at me wearily.

'You again?'

'Yes, madam. May I come in?'

She shrugged and held the door open. 'That stupid girl Susan's gone,' she said.

'Where's the watchman?'

'Drinking and farting in the kitchen.' She led me past the ancient tapestry into the dowdy parlour and stood there waiting for me to speak.

'Any more news on the house?' I asked.

'Yes, it's mine. I've seen Serjeant's Marchamount's lawyer.' She laughed bitterly. 'For what it's worth. I'll need to take in lodgers – a fine class of tenant I'll get in this mouldy hole. He had my money, you know.'

'Who?'

'Michael. When we married he got a big dowry from my father, to get me off his hands. That's all gone and this is how I'm left. He couldn't even bring any decent furniture from the monasteries, just that ugly old wall hanging. Did you see that whore?' she concluded bluntly.

'Not yet. But I have a query, madam. I believe Sepultus may have worked with a founder in his recent experiments.'

The frightened look that came into her face told me I had hit the mark. Her voice rose.

'I've told you: I'd no interest in his mad doings beyond worrying he'd blow up the house. Why are you asking me these questions? I'm a poor widow alone!'

'You are keeping something back, madam,' I said. 'I must know what it is.'

But she had stopped listening. She was staring out at the garden, her eyes wide. 'It's him again,' she whispered.

I whirled round. A gate in the wall was open and a man was standing there. I dreaded seeing the pockmarked man but it was a stocky, dark-haired young fellow who stood there. Seeing us looking, he turned and fled. I stepped to the door, then paused. Even if I caught him, what then? He could overpower me easily. I turned back to Goodwife Gristwood. She had sat down at the table and was crying, her thin body wrenched with sobs. I waited until she calmed down.

'You know who that man was, madam?' I asked sternly.

She raised a piteous face to me. 'No! No! Why do you try to catch me in these coils? I saw him watching the house yesterday. He was there all afternoon, just watching, he near scared the wits from me. He's one of the men who killed Michael, isn't he?'

'I don't know, madam. But you should tell your watchman.'

'This is punishment for my sin,' she whispered. 'God is punishing me.'

'What sin?' I asked sharply.

She took a deep breath, then looked me hard in the eye. 'When I was young, Master Shardlake, I was a plain girl. Plain, but full of base lusts and when I was fifteen I romped with an apprentice.'

I had forgotten how coarse her tongue was.

'I had a child.'

'Ah.'

'I had to give him away and do hard penance, confessing my sin in church before the congregation, saying how unclean I was Sunday after Sunday. The old religion was no gentler than the new when it came to sins of the flesh.'