“I see,” I replied, bowing my head to show that I had not meant to insult him.

“It is necessary to add new lands,” Subotai went on, in a rare mood of explaining things to an outsider. “That is the wisdom of the old High Khan. That is why we have no jealousy or conflict among ourselves. The Yassa that he gave us instructs us to conquer other peoples. As long as we do so, we will not fight among ourselves.”

I was beginning to understand. The Mongols’ empire was the creation of Genghis Khan, who was so revered by these warriors that they would not willingly mention his name. It was a model of dynamic social stability: as long as it kept expanding, it would remain stable at its core. That was why Subotai was driven westward; everything to the east as far as the Pacific coast was already under Mongol sway.

“Besides,” Subotai added, as if able to read my thoughts, “it makes me happy to see new lands and strange sights. I yearn to see this western ocean you speak of, and the lands beyond it.”

It was difficult not to admire him. “But, my lord general, the kingdoms of Europe will raise huge armies to oppose you — thousands of knights and tens of thousands of men-at-arms…”

Subotai actually laughed, a rare loosening of his self-discipline. “Do not try to frighten me, Orion. I have seen armies against me before. Did I ever tell you the story of the Battle of the Carts? Or our first battle against the host of Kharesm?”

And so it went for three days and long into each night. In his simple and straightforward way, Subotai was gathering intelligence and planning his next campaign. I felt twinges of conscience in giving him the information he needed, but I knew from my memory of the twentieth century that the Mongols never conquered Europe.

As our third session seemed to peter out to its natural conclusion, close to midnight, I told him that now he knew as much about Europe as I did, and there was no point in delaying me here further.

“Ahriman has a long lead on me, and he will arrive in Karakorum to do his evil work before I have a chance to stop him.”

Subotai seemed unconvinced about Ahriman’s evil, but, practical soldier that he was, he appeared perfectly content to let Ahriman and me fight that battle between ourselves.

“Ahriman heads toward Karakorum with a treasure caravan,” he told me, “that is only as swift as its most heavily laden camel. How good a rider are you?”

As far as I knew, I had never been on a horse. But I had seen others ride, and I knew that what they could do I could train myself to do in a day or less.

“I can ride,” I said.

“Good. We can send you to Karakorum by the yam.”

I was unfamiliar with the word. Subotai explained that it was a horse-post system, almost exactly like the Pony Express that would be reinvented in the American West six and a half centuries later. Barbarians the Mongols might be, but their post system was the most efficient communications network in the world. And the safest. The law of the Mongols, the Yassa, ruled the empire with a grip of steel. It was said that a virgin carrying a sack of gold could ride from one end of the empire to the other without being molested. And, I found, it was true.

When I returned to Agla’s yurt that night and woke her to tell her that I was leaving in the morning, she nodded sleepily and lifted the quilted blanket that was covering her.

“Get to sleep, then,” she said drowsily. “We’ll have a long day ahead of us, tomorrow.”

“We?”

“I am riding to Karakorum with you, of course.”

“But… will Hulagu allow you to leave?”

If she hadn’t been half asleep she would probably have been indignant. “I’m not a slave. I can go as I please.”

“It will be a difficult journey. We’re riding the horse-post. We’ll be on horseback all day, every day, for weeks.”

She smiled, closed her eyes, and muttered, “I’m better padded for that than you are.” And went back to sleep.

It was a grueling trip. In the twentieth century, travelers thought themselves rugged to endure the ride across Asia on the Trans-Siberian Railway from Moscow to Vladivostok. Agla and I rode horseback the same distance, across a more difficult route, crossing deserts and high, ice-draped mountain passes as we made our way across the Roof of the World and into the vast wilderness of the Gobi. By ourselves, we would have perished in less than a week. But the entire route was marked by a chain of Mongol posts, each a hard day’s ride from the last one, where we could get hot food, good water, and fresh ponies. Old or crippled warriors kept each post, usually aided by a few local youths who tended the corrals of horses. It was a monument to the power of the Mongols that no one ever attacked these posts. There seemed to be no underground resistance to the empire. Probably the people, remembering the terrifying massacres that accompanied the Mongol armies, were cowed to passivity. But perhaps the laws of the Yassa, and the tolerant rule of the Mongols once they had conquered a territory, kept their empire peaceful.

I had hoped to catch up with the caravan that Ahriman had taken, but the horse-post generally used a different, more direct route. Swift ponies with expert riders could tackle terrain that a camel caravan would never dare try to cross. Here and there we crossed the ancient caravan route. Even from miles away we could see the well-marked path that millennia of camels, oxen, and asses had beaten into the grassland. Twice we met caravans, long strings of beasts of burden heaped with treasures looted from the West, tinkling and jingling as they made their slow, patient way to Karakorum. Only a handful of warriors rode along as guards. No one in his right mind attacked a Mongol caravan; whole tribes could be exterminated for such a crime.

I asked, I searched for Ahriman, but he was not in either caravan. Which meant that he was even farther ahead of me than I had feared.

One night, after we had come down from the icy passes of the Tien Shan mountains and were safely housed for the night in the rude hut that passed for guest quarters at one of the post stations, I asked Agla why she had denied seeing Ahriman in Hulagu’s camp.

“I did not see him,” she said.

“But you knew he was there, didn’t you? Even in a camp as large as Hulagu’s, the presence of such a man would be known to everyone.”

“Yes,” she admitted, “I knew he was there.”

“Then why did you lie to me?”

Her chin went up a notch. “I did not lie. You asked me if I had seen him and I told you the truth: I had not. The Dark One stayed in the tent of Subotai. I never set eyes on him.”

“But you knew he was there.”

“And I knew that he had prophesied to Hulagu that you would come to the camp. And that he warned Hulagu that you were a demon and advised him to kill you,” Agla said. There was no shame in her expression, no guilt. “I knew that they had almost succeeded. And I knew that as long as you were under the lord Subotai’s protection, no further harm would come to you. Who do you think found you, dying in the dust behind the dung heap? Who do you think brought Subotai to you and convinced him that you were too valuable to be allowed to die?”

“You did that?”

“Yes.”

“But why? You didn’t know who I was or why I had come to…”

“I knew enough,” Agla said, her gray eyes shining in the light of the fire that crackled in the hearth. “I had heard that a strange man of great power had been brought into the camp and that Hulagu was fearful enough to listen to the Dark One’s warning. I knew that you were the man I have waited for all my life.”

“So you saved my life and protected me until I was well.”

She nodded. “As I will protect you with all my power once we reach Ogotai’s court in Karakorum.”

“Ahriman will be there,” I said.

“Yes. And he will try to kill you again.”