“Seventeen?” Jack and Eliza said in unison-both of them had to step lively, now, to keep pace with the Doctor as he stomped out of the Jahrmarkt making good time on those high heels. He wasn’t a big man but he had a fine set of calves on him, which his stockings showed off nicely.

“Dyadic, or binary numbers-old news,” the Doctor said, waving a hand in the air so that the lace cuff flopped around. “My late friend and colleague Mr. John Wilkins published a cryptographic system based on this more than forty years ago in his great Cryptonomicon -unauthorized Dutch editions of it are still available over yonder in the Booksellers’ Quarter should you desire. But what I take away from the Chinese method of fortune-telling is the notion of producing random numbers by the dyadic technique, and by this Wilkins’s system could be incomparably strengthened.” All of which was like the baying of hounds to Jack.

“Crypto, graphy… writing of secrets?” Eliza guessed.

“Yes-an unfortunate necessity in these times,” the Doctor said.

About now, they escaped the closeness of the Fun Fair and stopped in an open square near a church. “Nicolaikirche-I was baptized there,” the Doctor said. “ Kuxen!A topic strangely related to dyadic numbers in that the number of Kuxen in a particular mine is always a power of two, videlicet: one, two, four, eight, sixteen… But that is a mathematical curiosity in which you’ll have little interest. I am selling them. Should you buy them? Formerly a prosperous industry, upon which the fortunes of great families such as the Fuggers and Hacklhebers were founded, silver mining was laid low by the Thirty Years’ War and the discovery, by the Spaniards, of very rich deposits at Potosi in Peru and Guanajuato in Mexico. Buying Kuxen in a European mine that is run along traditional lines, as is done in the Ore Range, would be a waste of the lady’s money. But my mines or I should say the mines of the House of Brunswick-Luneburg, which I have been given the responsibility to manage, will be, I think, a better investment.”

“Why?” Eliza asked.

“It is extremely difficult to explain.”

“Oh, but you’re so good at explaining things…”

“You really must leave the flattery to me, milady, as you are more deserving of it. No, it has to do with certain new sorts of engines, of my own design, and new techniques for extracting metal from ore, devised by a very wise and, as alchemists go, non-fraudulent alchemist of my acquaintance. But a woman of your conspicuous acumen would never exchange her coins-”

“Silk, actually,” Jack inserted, turning half round to flash the goods.

“Er… lovely silks, then, for Kuxen in my mine, just because I said these things in a market.”

“Probably true,” Eliza admitted.

“You would have to inspect the works first. Which I invite you to do… we leave tomorrow… but if you could exchange your goods for coin first it would be-”

“Wait!” Jack said, it being his personal duty to play the role of coarse, armed bumpkin. Giving Eliza the opportunity to say: “Good Doctor, my interest in the subject was just a womanish velleity-forgive me for wasting your time-”

“But why bother talking to me at all then? You must’ve had some reason. Come on, it’ll be fun.”

“Where is it?” Jack asked.

“The lovely Harz Mountains-a few days’ journey west of here.”

“That’d be in the general direction of Amsterdam, then?”

“Young sir, when I spied your Turkish sword, I took you for some sort of Janissary, but your knowledge of the lands to the West proves otherwise-even if your East London accent hadn’t already given you away.”

“Uh, okay, so that’s a yes, then,” Jack mumbled, leading Eliza a few paces away. “A free ride in the Doctor’s train-can’t be too much wrong with that.”

“He’s up to something,” Eliza protested.

“So are we, lass-it’s not a crime.”

Eventually she wafted back over to the Doctor and allowed as how she’d be willing to “leave my entourage behind” for a few days, with the exception of “my faithful manservant and bodyguard,” and “detour to the Harz Mountains” to inspect the works. They talked, for a while, in French.

“He says a lot in a hurry sometimes,” Eliza told Jack as they followed the Doctor, at a distance, down a street of great trading-houses. “I tried to find out approximately what a kux would cost-he said not to worry.”

“Funny, from a man who claims he’s trying to raise money…”

“He said that the reason he first took me for Parisian was that ostrich plumes, like the sample in my hat, are in high fashion there just now.”

“More flattery.”

“No-his way of telling me that we should ask a high price.”

“Where’s he taking us?”

“The House of the Golden Mercury, which is the factory of the von Hacklheber family.”

“We’ve already been kicked out of there.”

“He’s going to get us in.”

AND THAT HE DID,by means of a mysterious conversation that took place inside the factory, out of their view. This was the biggest courtyard they’d seen in Leipzig: narrow but long, lined with vaulted arcades on both sides, a dozen cranes active at once elevating goods that the von Hacklhebers expected to rise in price, and letting down ones they thought had reached their peak. At the end nearest the street, mounted to the wall above the entry arch, was a skinny three-story-high structure cantilevered outwards over the yard, like balconies on three consecutive floors all merged into one tower. It was enclosed with windows all round except on the top floor, where a golden roof sheltered an open platform and supported a pair of obscenely long-necked gargoyles poised to vomit rain (should it rain) out onto the traders below. “Reminds me of the castle on the butt-end of a galleon,” was Eliza’s comment, and it wasn’t for a few minutes that Jack understood that this was a reminder of the naughty business off Qwghlm years ago, and (therefore) her oblique female way of saying she didn’t like it. This despite the gold-plated Mercury, the size of a man, bracketed to it, which seemed to be springing into flight above their heads, holding out a golden stick twined about with snakes and surmounted by a pair of wings. “No, it’s a Cathedral of Mercury,” Jack decided, trying to get her mind off the galleon. “Your Cathedral of Jesus is cross-shaped. This one takes its plan from that stick in his hand-long and slender-the vaults on the sides like the snakes’ loops. The wings of the factory spreading out from the head of it, where is mounted the bishop’s pulpit, and all of us believers crowded in below to celebrate the Messe. ”

Eliza sold the stuff. Jack assumed she sold it well. He knew they were soon to leave Leipzig and so amused himself by looking around. Watching the bales and casks ascend and descend on their ropes, his eye was drawn to a detail: from many of the countless windows that lined the courtyard, short rods projected horizontally into the air, and mounted to their ends, on ball-joints like the one where the thigh-bone meets the pelvis, were mirrors about a foot square, canted at diverse angles. When he first noticed them Jack supposed that they were a clever trick for reflecting sunlight into those many dim offices. But looking again he saw that they shifted frequently, and that their silvered faces were always aimed down toward the courtyard. There were scores of them. Jack never glimpsed the watchers who lurked in the dark rooms.

Later he chanced to look up at the highest balcony, and discovered a new gargoyle looking back at him: this was made of flesh and blood, a stout man who hadn’t bothered to cover his partly bald, partly grizzled head. He had battled smallpox and won at the cost of whatever good or even bad looks he might ever have had. Quite a few decades of good living had put a lot of weight into his face and drawn the pocked flesh downwards into jowls and wattles and chins, lumpy as cargo nets. He was giving Eliza a look that Jack did not find suitable. Up there on that balcony he was such an arresting presence that Jack did not notice, for a few minutes, that another man, much more finely turned out, was up there, too: the Doctor, talking in the relentless way of one who’s requesting a favor, and gesturing so that those white lace cuffs seemed to flit around him like a pair of doves.