“Ahriman is from Persia,” I said.

“So he freely admits. But he says that you are, too. Which you deny.”

“Assassins nearly killed me today.”

The mandarin made a small shrug. “That could have been a clever ruse, to put us off our guard. The two dead men were not Mongols, despite their garb. They could easily have been Persians. You may have killed them to keep suspicion away from yourself.”

“But I did not. They tried to kill me.”

The mandarin’s wrinkled face looked truly troubled. “I want to believe you, Orion. But I do not dare to act naïvely. I am convinced that either you or Ahriman is an assassin, perhaps even the very leader of the cult, the man known to the Persians only as the Old Man of the Mountains.”

“How can I convince you…?”

With a shake of his head, Ye Liu Chutsai said, “In a problem such as this, the Mongols would act with wonderful simplicity. They would simply kill both you and Ahriman — and possibly you, too, my dear lady — and have done with it. I, with my civilized conscience, will endeavor to determine which of you is the assassin and which is the innocent party.”

“Then I have nothing to fear,” I said, wishing that I actually felt that way.

“Not from me. Not yet.” The mandarin hesitated, then added, “But Ogotai is not a patient man. He may apply the Mongol solution and be rid of the problem once and for all.”

Agla and I were not exactly prisoners, but wherever we went in Karakorum, the same two Mongol warriors followed us. Ye Liu Chutsai said they were guards, for our protection, but they made me feel uneasy. Day and night they were never more than a few swift strides away. I learned that Mongol discipline was relentless: these men would guard us until they were ordered to stop. If we escaped their sight, they would be killed. If one of them died while guarding us, his son would take his place in such duty, if he had a son old enough to be a warrior. If not, his closest male relative would step in.

We had the freedom of the city, except for the one place I wanted to go — the pavilion of the High Khan, the ordu of silk-draped tents that I could see from the door of our quarters each morning. Ye Liu Chutsai would not permit me to see the Khan or to come any closer to Ogotai than the edge of the wide cleared space that marked the ordu. The mandarin still worried that I might be an assassin, or even the leader of the entire cult of assassins. So I was kept from seeing the High Khan while Chinese court intrigues began to weave their way through the ordu of the Mongols.

But there was nothing to prevent me from seeking out Ahriman. For days Agla and I wandered through the crowded, noisy lanes that meandered between yurts and buildings of stone and adobe, seeking the Dark One.Karakorum was a metropolis built by accident, without plan, without facilities. The Mongols saw it as merely another encampment, larger than any previous collection of yurts and carts that they had known. But they could not understand the differences that a change of scale makes. A nomad’s encampment of a thousand families with their tents and ponies and livestock could live beside a river for weeks on end before it had to move on. But a city of ten thousand families, or a hundred thousand, which remained fixed in one place, was beyond the ability of the Mongols.

Sanitation was nonexistent. To these nomadic warriors and herdsmen, who rubbed animal fat on their bodies to protect themselves from winter’s cold, bathing was almost unheard of. Garbage and human wastes were simply dumped on the ground, usually behind one’s tent. Water was carried to the city on the backs of slaves, taken from the same river into which the runoff from the waste dumps ran. That system worked for a temporary camp, but for a permanent city it meant disease, inevitably. I began to wonder how long it would take for Karakorum to be swept away by an epidemic of typhus. Perhaps that was what eventually ended the Mongol empire.

The noise of those twisting narrow streets rivaled twentieth-century Manhattan. Nobody spoke in tones lower than a shout. Ox-drawn carts creaked and groaned under heavy loads. Horsemen clattered by, scattering merchants, women, children and anyone else who happened to be in their way. It seldom rained, but when it did, thunder bursts poured torrents on the city. Almost every storm knocked down one flimsy adobe building or another, although the round felt yurts and the big tents of the ordu seemed to make it through the wind and rain better than the “permanent” buildings did. After each thunderstorm there were puddles everywhere, in which king-sized mosquitoes bred.

No one I spoke to admitted to knowing of the Dark One. Ye Liu Chutsai had met Ahriman, and told me that he had even spoken with Ogotai before I had arrived in Karakorum. But the mandarin would give me no hint as to where to find Ahriman.

So, day after day, Agla and I, trailed by our two faithful warrior guards, made our way through the bustling, noisy capital of the Mongols, shouldering and elbowing through the thick crowds, seeking one man in a city that must have numbered close to a million.

I tried every church we could find, from the foul-smelling hut of some Christian hermits to the golden magnificence of a Buddhist temple.

After nearly a week of searching, I finally saw what I had been looking for — a small, windowless, squat building made of gray stone, far off on the outskirts of the city, out near the corrals and barns where the stench of the animals and the droning buzz of the flies that lived off them were overpowering.

Agla’s face showed her disgust at the surroundings. “There’s nothing here but filth and smell,” she said.

“And Ahriman.” I pointed to the gray stone building.

“There?”

“I’m sure of it.” Turning to our guards, I asked, “What building is that?”

They glanced at each other before shrugging their shoulders and pretending not to know. Perhaps they were under orders to keep me away from Ahriman. Perhaps they were afraid of entering the Dark One’s domain. No matter. I headed straight for the low, wide door — the only opening in the building that I could see.

“That is not a good place to enter,” said one of our guards. It was the longest string of words I had ever heard him utter.

“You can wait outside,” I said, without breaking stride.

“Wait,” he said, hurrying to get in front of me.

“I’m going in. Don’t try to stop me.”

He was clearly unhappy with the idea, but equally unwilling to challenge me. He had been told what I had done to the two assassins. He sent his partner around to check on the building’s other entrances. There were none. Satisfied that he could watch the solitary door, he stepped aside.

“You must call me if there is danger,” he said.

Agla replied, “I will call, never fear.” But the warrior paid no attention to a woman.

I had to duck to get through the low doorway. Inside, the chamber was dark, gloomy. Agla pressed against me.

“I can’t see a thing,” she whispered.

But I could. My eyesight adjusted to the darkness immediately, and even though the chamber remained shrouded in murky shadows, I could make out a stone altar on a slightly raised platform, with strange symbols carved on stone above it.

“I’ve been expecting you,” Ahriman’s harsh, rasping voice rumbled.

I turned toward the sound and saw him, a darker presence among the deepest shadows in the far corner of the chamber.

“Come to me,” he said. “The girl will not be harmed; you can leave her there.”

Agla seemed to have frozen into lifelessness. She stood stock-still, clutching my arms, staring ahead blindly into the darkness.

“She will neither see nor hear anything,” Ahriman told me. “Leave her and come to me.”

I disengaged my arm from Agla’s grasp. She was still warm and alive, but I could detect no breath in her, no heartbeat.