I crossed to the window and looked out at the yard, surprised to see that both the flagstones and the high walls were stained black. 'Has there been a fire here?' I asked Susan.

'Master Sepultus did experiments out there sometimes, sir. Terrible bangs and hissings there were.' She crossed herself. 'I was glad he wouldn't let me see.'

Goodwife Gristwood spoke again. 'Yes, we were kept out of our own kitchen when he and my husband were at their foolery.'

I looked again at the scorch marks. 'Did they go out there often?'

'Only recently, sir,' Susan said. She turned to her mistress. 'I'll make an infusion, madam, it might ease us. Would you like some, sir? I have some marigolds-'

'No, thank you.'

We sat together in silence for a while. My mind was racing. It struck me that the formula might still be in the workshop, perhaps even with some samples of this Greek Fire. Now was a chance to look before the room was disturbed further, though I shrank from returning there. I bade the women stay in the kitchen and mounted the stairs again.

I stood in the doorway for a moment, steeling myself to look again at those terrible carcasses. Poor Michael had been in his mid-thirties, I recalled, younger than me. The afternoon sun was shining into the room, a sunbeam illuminating his dead face. I remembered that dinner in Lincoln's Inn Hall, how I had thought he had the questing, nosy look of an amiable rodent. I turned away from his look of terror.

There was a terrible casualness about the way the two men had been smashed down. It seemed the killers had simply staved in the doors and then felled the brothers like animals, with an axe blow each. They had probably been watching the house, waiting for the women to leave. I wondered if Michael and Sepultus, hearing the front door broken in, had locked themselves in the workshop in a vain attempt to save themselves.

I noticed Michael was wearing a rough smock over his shirt. Perhaps he had been helping his brother. But with what? I looked around. I had never been in an alchemist's workshop – I gave such people a wide berth, for they were known as great frauds – but I had seen pictures of their laboratories and something was missing. Frowning, I walked over to a wall lined with shelves, my feet crunching on broken glass. One shelf was full of books but the others were empty. From round marks in the dust I guessed jars and bottles had been stored there. That was what I had seen in the pictures, alchemists' chambers full of bottles of liquids and powders. There was nothing like that here. In the pictures there had also been benches with oddly shaped retorts for distillation – that would explain all the broken glass on the floor. 'They took his potions,' I murmured.

I took one of the books from the shelves, Epitome Corpus Hermeticum, and flicked through it. A marked passage read: 'Distillation is the elevation of the essence of a dry thing, by fire, thus by fire we come to the essence of things, even while all else be consumed.' I shook my head and put it down, turning to the remains of the chest. I saw that the fireplace and the wall behind it were fire-blackened like the yard.

The contents of the chest lay scattered all over the floor – letters and documents, one or two with bloody thumb prints on them. So the killers had searched through the contents. There was a document dated three years ago, conveying the house to Sepultus and Michael Gristwood, and a marriage contract between Michael Gristwood and Jane Storey drawn up ten years earlier. Under it Jane's father contracted to leave all his property to his son-in-law on his death, an unusually generous provision.

Something else on the floor caught my eye. I bent down and picked up a gold angel; it had fallen from a leather bag nearby that contained twenty more. The brothers' money had been left behind. Well, I thought, that was not what the killers were after. I rose, pocketing the coin. Another smell was beginning to overlay the sulphurous stink in the room, the sweet, rich smell of decay. I stepped on something that crunched under my heel and, looking down, saw I had broken a delicate set of scales. Sepultus's alchemist's balance. Well, he would not be needing it now. With a last glance at the bloody remains, I left the room.

JANE GRISTWOOD sat where I had left her, Susan beside her sipping something from a wooden cup. Susan looked up nervously as I came in. I took the gold coin and laid it in front of her mistress. She looked up at me.

'What's this?'

'I found it upstairs, in the remains of your husband's chest. There is a whole purse of angels there, together with the deeds to the house and other papers. You should keep them safe.'

She nodded. 'The deeds to the house. I suppose it's mine now. Great broken-down place; I never wanted it.'

'Yes, it will come to you now unless Michael had sons.'

'He had no sons.' She spoke with sudden bitterness, then looked up at me. 'You know the law then. You know about inheritance.'

'I am a barrister, madam.' I spoke sharply, for her coldness was beginning to repel me as it had Barak. 'You may care to fetch the gold and those papers; there will be others poking around this house soon.'

She stared at me for a moment. 'I can't go up there,' she whispered. Then her eyes widened and her voice rose to a shriek. 'Don't make me go up there; for pity's sake, don't make me see them again!' She began sobbing, a desperate howling like an animal caught in a trap. The girl took her hand again.

'I will fetch them,' I said, ashamed of my earlier curtness. I went back upstairs and drew the papers and the gold purse together. In the hot afternoon the smell of death was growing stronger. As I stood up I nearly slipped. I looked down, fearing I had slithered in the blood, but saw there was a patch of something else by the fireplace; a little pool of viscous, colourless liquid that had spilled from a small glass bottle that lay on its side on the floor. I bent down and dipped my finger in it. I rubbed my fingers together, it had a slippery feel. I sniffed. The stuff was odourless, like water. I righted the bottle and replaced the stopper that had fallen off in the struggle and lay nearby. There was no label to identify the thick, clear liquid inside. Hesitantly, I touched the tip of my tongue to it, then jerked back as a stinging, bitter taste filled my mouth, making me gasp and cough.

I heard footsteps outside and crossed to the window, dabbing at my burning mouth. Barak was outside with half a dozen men in Cromwell's livery carrying swords. I hastened downstairs as they marched in, their feet clumping heavily on the boards as they hurried to the kitchen. As I ran downstairs I heard Susan give a little scream. The men had crowded in; Goodwife Gristwood was frowning at them. Barak saw the little pile of papers I carried. 'What are those?' he asked sharply.

'Family papers and some gold. They were in the chest upstairs. I fetched them for Goodwife Gristwood.'

'Let me see.'

I frowned as he grabbed the papers. At least, I thought, the churl can read. He opened the bag of gold and examined the contents. Satisfied, he laid the gold and papers before Goodwife Gristwood. She clutched them to her. Barak looked at me.

'Any sign of the formula up there?'

'Not that I can see. If it was in that chest they took it.'

He turned to Jane Gristwood. 'Do you know anything about a paper your husband and his brother had, a formula they were working on?'

She shook her head wearily. 'No. They told me nothing of what they did. Only that they were engaged on some work for Lord Cromwell. I didn't want to know.'

'These men are going to have to search your house from top to bottom,' he said. 'It's important we find that paper. Afterwards two of them will stay here with you.'