Cromwell nodded. 'He did. To help Richard Rich pull in the proceeds of the dissolution.' He made a steeple of his fingers and looked at me over them.

'Last year, when St Bartholomew's priory in Smithfield surrendered to the king, Gristwood was sent to supervise the taking of the inventory of chattels to go to the king.'

I nodded. The hospital priory had been a large monastic house. I recalled the prior had been in league with Cromwell and Rich, and as a reward had been granted most of the priory lands. So much for vows of poverty. Yet they said Prior Fuller was dying, of a wasting disease God had laid on him for closing the hospital. Others said that Richard Rich, who had moved into the prior's fine house himself, was slowly poisoning him.

'Gristwood took some Augmentations men with him,' Cromwell continued, 'to quantify the furniture, the plate to be melted down and so on. He took the monastery librarian to show him what books might be worth keeping. The Augmentations men are thorough: they poke into nooks and crannies the monks themselves have often forgotten.'

'I know.'

'And in the crypt under the church, in a cobwebby comer, they found something.' He leaned forward, the hard dark eyes seeming to bore into mine. 'Something that was lost to man centuries ago, something that has become little more than a legend and a diversion for alchemists.'

I stared at him in astonishment. I had not expected this. He laughed uneasily. 'Sounds like a mummers' tale, eh? Tell me, Matthew, have you ever heard of Greek Fire?'

'I'm not sure.' I frowned. 'The name is vaguely familiar.'

'I knew nothing of it myself until a few weeks ago. Greek Fire was an unknown liquid that the Byzantine emperors used in warfare against the infidel eight hundred years ago. They fired it at enemy ships and it would set them ablaze from end to end, a rushing inextinguishable fire. It could burn even on water. The formula for its creation was kept a close secret, passed down from one Byzantine emperor to another till in the end it was lost. The alchemists have been after it for hundreds of years but they've never fathomed it. Here, Grey.' He snapped his fingers and the clerk rose from his desk and put a piece of parchment in his master's hands. 'Handle it carefully, Matthew,' Cromwell murmured. 'It is very old.'

I took the parchment from him. It was frayed at the edges and torn at the top. Above some words in Greek was a richly painted picture without perspective, such as the old monks used to illustrate their books. Two oared ships of ancient design faced each other across a stretch of water. At the front of one ship a golden pipe was belching red tongues of fire, engulfing the other.

'This looks like a monkish thing,' I said.

He nodded. 'So it is.' He paused, collecting his thoughts. I glanced at Barak. His face was sober, nothing mocking in it now. Grey stood beside me, looking at the parchment, his hands folded.

Cromwell spoke again, quietly though there were only the three of us to hear. 'Friend Gristwood was at St Bartholomew's one day last autumn when he was called to the church by one of the Augmentations clerks. Among the old lumber in the crypt they had found a large barrel, which, when they opened it, proved to be full of a thick, dark liquid with a terrible smell, like the stench of Lucifer's privy Gristwood said. Michael Gristwood had never seen anything remotely like it before and he was curious. There was a plaque on the barrel, with a name, Alan St John. And some Latin words. Lupus est homo homini.'

'Man is wolf to man.'

'Those monks could never use plain English. Well, friend Gristwood thought to set the librarian to search for the name St John in the library. They found it in the catalogue and it led them to an ancient box of manuscripts about Greek Fire, deposited there by one Captain St John, who died in St Bartholomew's hospital a century ago. He was old soldier, a mercenary who was at Constantinople when it fell to the Turks. He left a memoir.' Cromwell raised his eyebrows. 'He told how a Byzantine librarian fleeing with him to the boats gave him the barrel, which he claimed contained the last of Greek Fire, together with the formula to make the substance. The librarian had found it when clearing out the emperor's library and gave it to St John so that at the last a Christian should have the secret, not the heathen Turks. You see the page is torn?'

'Yes.'

'Gristwood tore off the formula that was written in Greek above that picture, together with instructions for constructing the throwing apparatus used to project it. Of course, he should have brought it to me – it was monastic property and it belongs to the king now – but he didn't.' Cromwell frowned and his heavy jaw set. There was a moment's silence, and I realized I was twisting at my cap again. He went on in the same quiet voice.

'Michael Gristwood has an older brother. Samuel. Also known as Sepultus Gristwood the alchemist.'

'Sepultus,' I repeated. 'Latin for buried.'

'As in the buried knowledge only alchemists can divine. Yes, like most of those rogues he gave himself a fancy Latin name. But when Sepultus heard Michael's story, he realized the formula could be worth a fortune.'

I swallowed hard. I realized now how great this matter was.

'If it's genuine,' I said. 'Alchemists' formulae for the creation of wonders are ten a penny.'

'Oh, it's genuine,' he said. 'I've seen it used.'

Godless gesture though it was, I felt a sudden urge to cross myself.

'The Gristwoods must have spent some time making more of the stuff, for it was March this year before Michael Gristwood came to me. Not directly, of course, someone of his standing couldn't do that, but through intermediaries. One of whom brought me that parchment and the other documents from the convent. Everything but the formula. With a message from the Gristwood brothers that they had made Greek Fire, they were offering a demonstration and if I decided I wanted the formula they'd give it to me. In return for a licence on its development, so they'd have the exclusive right of manufacture.'

I looked at the parchment. 'But it didn't belong to him. As you said, as it was monastic property it is now the king's.'

He nodded. 'Yes. And I could have had the brothers brought to the Tower and the information forced out of them. That was my first reaction. But what if they fled before they could be arrested? What if they sold the formula to the French or the Spaniards? They're a tricky pair. I decided to play along at least until I'd seen what they could do; once I'd found out if there was anything in it I could promise them a licence, then have them arrested for theft when they were least expecting it.' He set his thin lips. 'That was my mistake.' He looked at Grey, still hovering beside me. 'Sit down, master clerk,' he snapped. 'You make me uneasy hovering there. Matthew can keep the parchment.'

Grey bowed and returned to his desk, where he sat expressionless. He must be used to bearing the brunt of Cromwell's temper. I saw Barak's eyes on his master, a look of almost filial concern in them. Cromwell leaned back again.

'England has lit a fire across Europe, Matthew, the first large state to break from Rome. The pope wants the French and Spanish to combine and overthrow us. They won't trade with us, there's undeclared war with the French in the Channel and we're having to plough half the revenues from the monasteries into defence. If you knew how much we've spent it would make your hair curl. The new forts along the coast, the building of ships and guns and cannon-'

'I know, my lord. Everyone is frightened of invasion.'

'Those who are loyal to reform, at least. You haven't turned papist since last we met, have you?' His stare took on a terrible intensity.

I squeezed the cap tightly. 'No, my lord.'