Timeline

"I understand now," Stern said. "And each of the tanks is different."

"Right. Each one is different."

It was, Stern thought, a classic real-world scientific problem. Weighing risks, weighing uncertainties. Most people never understood that the majority of scientific problems took this form. Acid rain, global warming, environmental cleanup, cancer risks  –  these complex questions were always a balancing act, a judgment call. How good was the research data? How trustworthy were the scientists who had done the work? How reliable was the computer simulation? How significant were the future projections? These questions arose again and again. Certainly the media never bothered with the complexities, since they made bad headlines. As a result, people thought science was cut and dried, in a way that it never was. Even the most established concepts  –  like the idea that germs cause disease  –  were not as thoroughly proven as people believed.

And in this particular instance, a case directly involving the safety of his friends, Stern was faced with layers of uncertainty. It was uncertain whether the tanks were safe. It was uncertain whether the control room would give adequate warning. It was uncertain whether they should fill the tanks slowly now, or quickly later. They were going to have to make a judgment call. And lives depended on that call.

Gordon was staring at him. Waiting.

"Are any of the tanks unpitted?" Stern said.

"Yes. Four."

"Then let’s fill those tanks now," Stern said. "And wait for the polarization analysis and the computer sim before filling the others."

Gordon nodded slowly. "Exactly what I think," he said.

Stern said, "What’s your best guess? Are the other tanks okay, or not?"

"My best guess," Gordon said, "is that they are. But we’ll know more in a couple of hours."

06:40:22

"Good Sir Andre, I pray you come this way," Guy de Malegant said with a gracious bow and a wave of his hand.

Marek tried to conceal his astonishment. When he had galloped into La Roque, he fully expected that Guy and his men would kill him at once. Instead, they were treating him deferentially, almost as an honored guest. He was now deep in the castle, in the innermost court, where he saw the great hall, already lit inside.

Malegant led him past the great hall and into a peculiar stone structure to the right. This building had windows fitted not only with wooden shutters but with windowpanes made of translucent pig bladders. There were candles in the windows, but they were outside the pig bladders, instead of inside the room itself.

He knew why even before he stepped into the building, which consisted of a single large room. Against the walls, gray fist-size cloth sacks stood heaped high on raised wooden platforms above the floor. In one corner, iron shot was piled in dark pyramids. The room had a distinctive smell  –  a sharp, dry odor  –  and Marek knew exactly where he was.

The arsenal.

Malegant said, "Well, Magister, we found one assistant to help you."

"I thank you for that." In the center of the room, Professor Edward Johnston sat cross-legged on the floor. Two stone basins containing mixtures of powder were set to one side. He held a third basin between his knees, and with a stone mortar, he was grinding a gray powder with a steady, circular motion. Johnston did not stop when he saw Marek. He did not register surprise at all.

"Hello, Andre," he said.

"Hello, Professor."

Still grinding: "You all right?"

"Yes, I’m okay. Hurt my leg a little." In fact, Marek’s leg was throbbing, but the wound was clean; the river had washed it thoroughly, and he expected it to heal in a few days.

The Professor continued to grind, patiently, ceaselessly. "That’s good, Andre," he said in the same calm voice. "Where are the others?"

"I don’t know about Chris," Marek said. He was thinking of how Chris had been covered with blood. "But Kate is okay, and she is going to find the – "

"That’s fine," the Professor said quietly, his eyes flicking up to Sir Guy. Changing the subject, he nodded to the bowl. "You know what I’m doing, of course?"

"Incorporating," Marek said. "Is the stuff any good?"

"It’s not bad, all things considered. It’s willow charcoal, which is ideal. The sulfur’s fairly pure, and the nitrate’s organic."

"Guano?"

"That’s right."

"So, it’s about what you’d expect," Marek said. One of the first things Marek had studied was the technology of gunpowder, a substance that first became widely employed in Europe in the fourteenth century. Gunpowder was one of those inventions, like the mill wheel or the automobile, that could not be identified with any particular person or place. The original recipe  –  one part charcoal, one part sulfur, six parts saltpeter  –  had come from China. But the details of how it had arrived in Europe were in dispute, as were the earliest uses of gunpowder, when it was employed less as an explosive than as an incendiary. Gunpowder was originally used in weapons when firearms meant "arms that make use of fire," and not the modern meaning of explosive projectile devices such as rifles and cannon.

This was because the earliest gunpowders were not very explosive, because the chemistry of the powder was not understood, and because the art hadn’t been developed yet. Gunpowder exploded when charcoal and sulfur burned extremely rapidly, the combustion enabled by a rich source of oxygen  –  namely nitrate salts, later called saltpeter. The most common source of nitrates was bat droppings from caves. In the early years, this guano was not refined at all, simply added to the mixture.