A divine healer, a general, a young marquis! Who can rival them!

Yang Hu spent half the night examining that small handful of dried grass leaves under the lamp.

The leaves were withered and brittle, but the veins were still visible, and the fine serrations around the edges became apparent after soaking. He crushed a leaf, put it in his mouth, and chewed it; the bitterness lingered on his tongue for a long time before dissipating. It was a mixture of purslane and iron amaranth, both folk remedies for dysentery, used by people in the countryside within the Great Wall when they had an upset stomach. These things didn't grow on the grasslands, and the barbarian shamans certainly wouldn't use them as medicine.

"These were brought from inside the Great Wall." He gathered the leaves back into the leather bag, looked up, and said, "They were brought there in a hurry, and weren't even fully dried before being packed away."

Su Heng sat opposite her, turning the leather pouch inside out to examine it. The leather cord at the opening was frayed. In the three years she had been investigating that hand, she had turned over countless small items like these. She could tell just by touching what items had been carried around for a long time and what items had been temporarily stuffed in.

"How long did the commotion last in their camp?"

"It's hard to say," Yang Hu said. "But such a small bag is only enough for one person to eat for three to five days. This shows two things: first, they are short of food; second, they are so short of food that they have to share it among themselves."

He didn't sleep that night. He went through the notebook he had kept for the past two months again, copying down the rise and fall of the epidemic in the city day by day onto another sheet of paper: which day had the most people, which day it peaked, which day it began to decline, and how many days had passed in between. After he finished copying it down, he stared at the string of numbers for a long time.

Inside the city, there were two thousand people. They had done everything they could—sealing the wells, boiling water, and isolating people—yet they still lost three hundred and seventeen lives. Outside the city, there were thirty thousand people, their bodies piled up, drinking the seeping water, their tents next to each other without even a ditch separating them.

The next morning, Yang Hu reported the matter to the central command tent.

The few officers still standing in the tent all had almost the same first reaction after hearing this: take advantage of their illness and attack them.

"Thirty thousand men, if dysentery breaks out, half of them will collapse in half a month." Captain Ma slammed his fist on the edge of the sand table, his eyes red. "If we dare to open the city gates and charge now, we could burn that entire camp down!"

"It cannot be opened."

It was Yang Hu who spoke. Everyone in the tent turned to look at him.

"Didn't you say they were having an outbreak?"

"That's precisely because of the commotion." Yang Hu walked to the sand table and pointed to the densely packed camps outside the city. "Dysentery spreads by water, by hand, and by people crowding together. Our people rush out, fight alongside their people, trample their ground, drink their water, and when they come back, they'll be carrying the plague into the city."

"So we'll just stand by and watch?"

"No." Yang Hu moved his finger three inches north, landing it on the ditch piled with corpses. "Let's see how they deal with this."

He reached into his robes, pulled out a piece of paper folded several times, and unfolded it, laying it on the table. The paper didn't depict a battle formation; instead, it showed three crooked, curved lines drawn with charcoal.

"This is the one in our city." He pointed to the longest one, "It started on the 14th, peaked on the 17th, and ended on the 22nd. It lasted eight days, and 317 people died."

He then pointed to a second, much shorter one: "This is what it looks like after we sealed the well, boiled the water, and isolated ourselves from others."

"And what about the third one?"

"The third rule is to not seal the wells, not boil water, and not isolate people." Yang Hu's fingertip traced the line that went straight up and never returned. "I've seen this rule in books, and I've also seen it in real life once. Thirty thousand people crammed into one place, drinking from the same source of water, with corpses piled up upwind. Half of them would collapse in a month."

The tent remained quiet for a long time.

The first to speak was Commandant Wang, his voice terribly hoarse: "You mean, there's no need to fight?"

"Hitting them will only slow them down." Yang Hu put the paper away. "What they need most right now isn't soldiers, but clean water and a cure for dysentery. We won't give them either of those."

"Why won't you give it to me?"

"The stream outside the city."

That stream comes down from the mountain pass to the north, and winds around the west wall of Qingshikou for three miles. It is the only flowing water in this area. Since the barbarians besieged the city, they have been drawing water from that section.

"The upstream of the stream is in our hands," Yang Hu said. "There's no need to poison it, and I won't either. As long as we block the water upstream and divert it to that low-lying area to the east, the downstream will be cut off within three days. If they want to drink water, they'll have to dig wells nearby. What they'll find is water that has seeped in from where the corpses were piled up."

Captain Ma's breathing became heavy.

"There's one more thing," Yang Hu said, "Release the sixty-odd prisoners we have in our hands."

This sentence caused an uproar inside the tent.

"Release them?" Captain Ma jumped to his feet. "Those are over sixty lives! If we let them go, they'll just turn around and climb back onto the city walls!"

"They can't get onto the city wall." Yang Hu looked at him. "Of these sixty-odd people, half of them had stomach problems, which we cured in the South Camp. They saw with their own eyes how we sealed the well, how we boiled water, and how we carried the dead out to be cremated. They also saw with their own eyes how the path on our wall got shorter day by day."

He paused for a moment.

"They'll go back and talk."

Commandant Wang suddenly understood.

The barbarians believed in witch doctors and divine punishment. When an epidemic broke out in the camp, the witch doctors would only perform rituals and claim it was a sin sent down by the Eternal Heaven. But when these sixty-odd men returned, they would say that the city inside the pass had also experienced an epidemic, but the city sealed its wells, boiled water, and suppressed it in twenty-two days.

Three hundred and seventeen died, not half of the thirty thousand.

"The morale of the army," Commander Wang said in a low voice.

"Morale." Yang Hu nodded. "Their witch doctors had no solution. But their people now know that there is a solution, it's just that their witch doctors don't have it."

"What if they kill those sixty-odd people as spies?" Commandant Wang asked.

"That's even better," Yang Hu said. "If we kill these sixty-odd people, the rest of the camp will know that anyone who mentions how to treat the plague in that city inside the pass will die. This can be suppressed for a while, but not for a month. When people are about to die, they will say anything."

The work of drawing water was done at night.

The upstream section is four miles from the city, in the northwest, near the foot of the mountain. Commandant Wang selected three hundred men, equipped with shovels and picks, and sneaked out in the latter half of the night. Yang Hu went with them. He didn't know how to dig a ditch, but he needed to see for himself whether the depression was deep enough and whether the water would flow back.

Over three nights, the stream changed course.

The release of prisoners took place on the afternoon of the fourth day. The city gate was opened a crack, and over sixty people walked out in a line, not one of them looking back. The last one at the end even turned back and bowed to the city wall. His festering leg was a wound that Yang Hu had personally cleaned.

From that day on, the camp outside the city began to change.

First, the water-fetching team moved further and further away, from the stream to the foot of a slope three miles away. Then, the camp began digging wells, seven or eight in total, all in low-lying areas.

On the ninth day, the barbarian camp began to move north.

On the morning of the fifteenth day, Su Heng ran down the horse path and lifted the tent flap, her face bearing an expression that Yang Hu had never seen before.

"Yang Hu," she called him by his first name for the first time, "Go up and take a look."

Yang Hu climbed up the eastern section of the city wall.

The 30,000-strong camp outside the city was a whole section shorter than it had been fifteen days ago. The banners were still there, the tents were still there, but the open spaces between the tents were larger, and the smoke from the cooking fires was thinner.

He stood behind the battlements, watching until the sun had fully risen. The wind came from the west, carrying the lingering smell of the abandoned camp, but this time, the smell drifted outwards and couldn't enter the city.

On the thirty-eighth day of the siege, more than 1,900 people stood on the city wall of Qingshikou.

The 30,000 men below the city walls are collapsing on their own.