Toria stifled her surprise at Rymark’s rare show of humility. Ellias sorted through the stack of parchments, his expression thoughtful, until he found one more smudged and yellowed than the rest. “I think this would be the best place to start.”
He pointed to a section of the parchment that contained two horizontal lines with a sinuous curve that joined them at the lower left and ran to the upper right.
“This is a model of the Darkwater’s contagion, according to the mathematicum,” he said. He put his finger on the curve between the second and third vertical lines. “This is where we’re at now.”
Toria had undertaken some rudimentary studies of the mathematicum a few decades ago when she was last placed in Moorclaire, but her talents ran toward others rather than logic and space. Even so, she recognized the curve. “I’m familiar with it,” she said. “It’s called the plague curve, though it goes by other names.”
Fess pointed to the first half of the graph, where the curve grew progressively steeper from left to right. “I’ve heard healers talk about this. They called it the kingdom killer.”
Ellias nodded his approval. “Perceptive and correct. The left-hand side of the curve describes what happens at the start of a plague, but to grasp the whole it will help to think of a hypothetical kingdom on a remote island. No one comes and no one can leave. Now, introduce a perfectly deadly plague.” He shrugged. “It doesn’t really matter which one.”
“Everyone would fall ill sooner or later,” Fess said.
“Exactly.” Ellias nodded. “At first the number of sick would be fairly small, but they would grow quickly. A healer might have two patients the first week and four the week after, but by the third week he would have eight and then sixteen by the fourth week.”
Ellias caught her eye. She knew what would come next. “The healer, if he’s new to his craft, might not suspect what shape the graph of the contagion must take. He might suppose the rate would continue as before, doubling every week.”
Fess pointed to the right-hand side of the graph. “Sooner or later, most of the kingdom has already been infected. The rate can’t double because over half the people have already caught the disease.”
Ellias nodded. “The young healer, seeing the rate of disease start to slow, becomes encouraged. He doesn’t realize his death sentence and that of everyone on the island has already been written.”
Fess looked back at the curve, and Toria saw his face grow pale. “You’re saying the evil of the Darkwater is like that?”
Ellias nodded. “Exactly. The northern continent is the island. It’s early, very early yet, but we’re locked in a battle that’s going badly.”
She leaned against the table. “I refuse to accept that defeat is inevitable. It isn’t.”
Rymark cocked his head at her. “There is a note of confidence in your voice, Lady Deel, in defiance of our explanation.”
Unwilling to explain or commit to Ealdor’s instruction, she turned away. “The assembled might and gifts of the entire north are bent to this task, Your Majesties. Surely you don’t think victory is impossible.”
Rymark and Ellias exchanged a glance, and both men sighed. “The issue is still in doubt, Lady Deel,” Rymark said. “We are still in the early part of the curve and have yet to reach the point of no return.”
Fess pointed to the exact middle of the diagram, where a point on the curve lay halfway between the two horizontal lines. “Is that here?”
Rymark’s voice rasped within the tent. “I wish it were.”
Ellias shook his head. “By that time, half our forces are infected and it’s too late. No. To defeat the forest, the poison’s momentum must be halted well before that.” He pulled an artist’s charcoal stick that had been sharpened to a fine point and drew a line that touched the curve near the left end, where it turned up to grow steeper. “If we reach this point, the war is lost. The momentum behind the forest will be too great to stop.”
“Then we must find a way to stop it,” Toria said.
Rymark shook his head. “Bravely spoken, but my men can’t see in the dark, Lady Deel, and the enemy can. It’s not just that we can’t fight what we can’t see, we can’t stop it either. At some point our forces will be too thin to reliably quarantine the forest.”
Fess pointed to the map. “Then have your patrols pull back from the forest.”
“That means they have to cover more ground,” Rymark said. “Not less.”
Fess nodded. “If you widen the ring around the forest enough, those who slip by the outer patrols won’t be able to make it to the boundary of the Darkwater before sunrise.”
“If we maintained an inner cordon as well, we would catch those heading for the forest during the daylight.”
“Your Majesty,” Maenelic said. “Is it a good idea to split your forces?”
“Not usually, no, but we’re in a most unusual war.” Rymark pursed his lips before turning to the king of Moorclaire. “You’re better at the numbers than I am, Ellias. Do we have enough men?”
He nodded. “For now, but it’s going to mean short rest and no reserves.”
Rymark turned to Fess. “It’s an unorthodox approach, but I find I’m more inclined to listen to new ideas of late.”
“‘Nothing gets a man’s attention,’” Fess murmured.
Rymark laughed, harsh, loud. “‘Like the prospect of death,’” he finished.
Toria nodded even as she managed to stifle a sigh. “Do those who venture into the forest strike singly, or do they coordinate their attacks?”
“Their strikes are random, Toria Deel,” Ellias said. “And there are fewer attacks than I would have thought.”
“Those who do strike are like an alchemist’s experiment gone wrong,” Rymark growled. “They move like gifted, creating explosions of violence and killing a squad or more before they can be put down. Some of the attackers are soldiers,
