‘Hurry, Perkyn. This night we shall be well rewarded for our pains.’

Jared laid out the elements neatly on the table.

Charcoal, small uniformly blackened twigs in a basket.

Sulphur, a startling pristine yellow in a basin.

The hsiao. Pure-white crystals that gleamed in the lamplight.

And then the mortar and pestle. Cleaned spotless, it had an iron bowl and bronze pestle, easily up to the job it faced now.

With Perkyn looking on nervously Jared started with the charcoal. Heaping it into the mortar he ground it down, feeling the gritty resistance gradually give as he worked.

The bowl was soon half-full of fine dust – with the same for the rest he would have plenty for the first trial. He set it aside and cleaned the bowl.

Then the sulphur. A careful crunch and twist, crunch and twist until it too was a fine-ground dust.

Finally the hsiao. He gave it everything he had until it fell through his fingers, a perfectly consistent waterfall of tiny glittering crystals.

‘And this is our finish, Perkyn,’ he announced gravely. ‘Each of these will now be brought to embrace the other closely, but when they are roused by fire, they fly apart in a terrible rage.’

Jared emptied in some ground charcoal to the bowl and added the sulphur, grinding away until the yellow swirl had been subsumed into a grey-black. Then the hsiao was ground into the mixture and when the result was a uniform dull-grey coarse dust with the barest suggestion of a sheen he stopped work.

It was done.

It looked like huo yao – and a tentative sniff instantly brought it all back to him. This was it!

Jared didn’t have bamboo but he’d made up some tubes from moulding clay of the same dimensions. He carefully poured the grey powder into one of them, sealed it with a twist of cloth and took it to the end of the cellar.

‘Perkyn. I’m now about to release the demons. It will be loud and dreadful – do stop your ears if you don’t want to be frightened.’

‘No, not yet – I’m going outside!’ he gulped and scrambled to get away.

So he would be the only witness. Jared shrugged, but there was no stopping now.

Setting the tube down on a shelf he took the lamp and taking a deep breath applied it to the cloth, then rapidly retreated.

He tensed for the shock.

The flame progressed merrily until it reached the end of the tube. It died momentarily – then there was only a feeble pop and show of flame and a suddenly mounting cloud of grey-white smoke.

Hardly believing what he’d seen he approached gingerly. The clay tube had split lengthways, revealing a blackish ash inside, but as a show of violence it was pitiful.

He’d followed everything scrupulously, and to be let down like this!

Jared paced up and down, barely noticing the rank stink that lay on the air. What could have gone wrong? He’d followed his mentally rehearsed instructions with meticulous attention and was certain that he’d missed nothing.

It just had to work – he’d try again with double the powder.

But this made no difference.

Was it the quality of the ingredients? With the possible exception of the hsiao they had been identical to Wang’s.

Was it that the tube had not been bamboo? The principle was to stop the fire-maddened elements fleeing each other until they’d called on heaven’s thunder to free them. This had been done.

Dispirited, Jared concluded it had to be the ingredients – and he’d have to start again from scratch.

He left the cellar heavily and saw Perkyn rise shamefacedly from behind a tombstone. They trudged home together.