'I travelled from Sussex to London in a crayer once.'

'You know what they're like then. Long, heavy barges. This one was a big solid thing, with sail and oars, that used to carry coal down the coast from Newcastle. Bonaventure, she was called.' He shook his head. 'She was to have an adventure all right.

'Like I said, my master chose this place because it was out of the way. He asked me to be here at first light on a March morning, when hopefully there wouldn't be any river traffic, and wait for him. He told me I might see something strange. "More likely, though," he said, "you won't."

'Anyway, I rode down here before dawn, and damned difficult it was, following the trackways through these marshes in the dark. The old crayer was where I'd moored her, for she wasn't worth anyone stealing. I tied Sukey up and walked about, stamping my feet to keep warm as the sun came up. The strange noises those river birds make as the day starts, they made me jump a few times.

'Then I heard horses' hooves, and a creaking sound, and through the reeds I saw my master approaching on horse-back. It was strange seeing him out there. He had a lowering look on him, kept glaring at the two men accompanying him. They were on horseback and one of the horses was pulling a cart with something heavy hidden under a pile of sacking.

'They got to the wharf at last and dismounted. I got a good look at the Gristwoods for the first time. I thought them poor folk, God rest them.'

I nodded. 'Michael was an unqualified attorney. The sort who deals with small cases, pushes business for the barristers.'

'Ay, I know that sort,' Barak said with a sudden sharpness that made me glance at him. 'They were both small, skinny men, kept glancing at my master with apprehensive looks. I could see he thought all this beneath his dignity; I thought if they didn't satisfy him they'd smart for it. One of the brothers wore a skullcap and a long alchemist's robe, the complete paraphernalia, for all that it was spattered with mud from his trip through the marshes. My master had on a simple black cloak, as he does when he travels alone. He introduced me to the Gristwoods and the pair doffed their caps and scraped to me like I was an earl.' He laughed. 'I thought they were the crookedest-looking pair of arseholes I'd ever seen.

'My master ordered me to tie the horses to posts by the shed, where I'd put Sukey. When I got back, the brothers were unloading their cart. I'd never seen such a pile of strange stuff: a long thin brass pipe and a big metal handpump like some of the conduits have. The earl came over and said quietly, "Look over that boat with me, Jack. I want to be sure there's no trickery." I dared to ask him what it was all about, and he looked dubiously to where the brothers were unloading an iron tank of some sort; by the way they were sweating and grunting there was something heavy inside. He told me then that Sepultus was an alchemist and had promised to show us a great wonder with that apparatus. He raised an eyebrow, then walked over to the boat.

'I helped him in and he looked the ship over from end to end. We even went down to the hold and walked about, coughing for there was a little coal dust. He said to look for trickery, anything strange. But there was nothing; it was just the empty old tub I'd bought cheap from the ship merchant.

'When we got back on deck the brothers had set up their apparatus on the jetty. The metal tank had been attached to the pump at one end and to the pipe at the other. I caught a whiff of something from the tank. It was like nothing I'd ever smelt before, a harsh tang that seemed to go right up your nostrils into your skull.'

'Tell me more about how the apparatus looked.'

'The pipe was about twelve feet long, and hollow, like a gun barrel. Under the end they'd fixed a wick, a pot of string greased with candle wax. The other end was fixed to the tank, as I said.'

'How big was the tank? Enough to hold, say, a large barrelful of liquid?'

He frowned. 'Yes. Though I don't know how full it was.'

'No. I'm sorry, go on.'

'When my master and I got back on land we saw they'd heaved the tank onto a big iron tripod. To my surprise, they were trying to light a fire of sticks underneath it now, fussing about with flints.

'Then Michael Gristwood gave a great shout of excitement. "It's lit!" he cried. "It's lit! Move away, my lord, away from the pipe!" My master looked scandalized at being addressed so familiarly, but went to stand behind the brothers. I went with him, wondering what on earth was to happen.'

Barak paused a moment. He looked out over the water, swirling with little gurgling eddies as the tide swept in again.

'It happened very quickly then. Michael took a twig from the fire and lit the wick, then ran back, and he and Sepultus worked the pump up and down. I saw a movement at the front of the pipe and then a great sheet of yellow flame, a dozen feet long, shot out with a roaring sound, flew through the air and hit the boat amidships. It seemed to twist in the air like a live thing.'

'Like fire from a dragon's mouth.'

He shivered. 'Ay. The wood caught light immediately, the flames seemed to stick to it and devour it like an animal eating its way along a carcass. Some of the flames fell down on the water and by the throat of God I saw the water burning. Saw it with my own eyes, a patch of flames leaping up and down on the river. For a minute I was terrified the whole river might burn up, fire leaping all the way to London.

'Then the brothers turned the pipe round at an angle, pumped again, and another long gout of flame, too bright to look at, shot out and hit the stern. It seemed to leap at it like something alive. The boat was burning merrily now. The heat from that flying fire was tremendous. I was twenty feet away but my face felt scorched. Another burst of fire, and another, and then the poor old crayer was blazing from end to end. Everywhere birds were clattering up from the marshes and flying off. By Jesu, I was frightened, I'm no godly man but I was praying to Our Lady and all the saints to protect me and if my master allowed rosaries I'd have been fondling the beads till they broke.

'We watched the boat, just a mass of flame now, clouds of thick black smoke rising into the sky. I looked at my master. He wasn't afraid, he just stood watching with his arms folded, a gleam of excitement in his eyes.

'Then I heard the screaming. I think it had been going on for a while but I hadn't noticed. It was the horses, they'd seen those huge gouts of leaping fire and they were terrified. I ran to them and they were kicking and flailing, trying to escape from the posts. I managed to calm them before they did themselves real harm, for I've a way with horses, and thank God there were no more sheets of flame; what was left of the boat was sinking now. When I went back to the jetty it had gone, even the rope holding it had burned away as you can see. My master was talking with the Gristwoods, who were looking pleased with themselves for all that their clothes clung to them with sweat. They began packing up their stuff.' He laughed and shook his head. 'The river was quiet again, the boat had sunk and the fire on the water had gone out, thank Christ. It was like nothing had ever happened: except a thirty-ton crayer had been burned to nothing in moments.' Barak took a deep breath and raised his eyebrows. 'And that's it, that's what I saw with my own eyes. Afterwards, when the Gristwoods had driven off again, my master told me that what I had seen was called Greek Fire, told me how Michael Gristwood had found the formula at Barry's, and swore me to secrecy.'

I nodded. I walked to the end of the jetty, Barak following. I looked down into the dark, heaving waters.

'Were you at the second demonstration?'

'No. My master commissioned me to find another, larger, ship, an old balinger, and have it taken here, but he attended that one alone. He told me the second ship was destroyed in exactly the same way.' He looked into the river. 'So there's the remains of two of them down there.'