Erhi cried out in surprise as a foot stepped through the portal. The foot materialised into a pair of legs, then a body and finally a man holding a spear. His features were familiar to Erhi from the dozens of enemy scouts whose heads had been brought into camp. He was a Khwarezmid, a Mamluk Turk, a Muslim. One of the people who had insulted the Great Khan by murdering his ambassadors. Noticing Erhi, the man raised his spear and uttered something in his language. Erhi had no way of understanding what he was saying but she recognised a threat when she saw one. Very slowly, she reached for her bow. The man repeated himself, louder this time, and brandished his spear in her direction.

Before Erhi could respond, there was a blur of movement and another body flew through the portal, crashing into the Khwarezmid. They tumbled onto the snowy ground. When they came to a rest, the Khwarezmid emerged on top, his hands wrapped around his attacker's throat. Erhi recognised the attacker as the boy she had seen from the night before. His face turned purple as his windpipe was crushed by the Khwarezmid. He beat his hands helplessly against the Khwarezmid's chest. It was clear he was no warrior. In another minute he would be dead.

Without thinking, Erhi drew an arrow from her quiver and took aim. The boy continued to thrash and claw at the hands encasing his throat. With each passing second he struggled less and less. The fight dying in his eyes as the air was squeezed from his lungs. Bucking against the ground, the boy made one final effort to throw off his attacker. The Khwarezmid reared up, trying to keep his weight pinioned on top of the boy. Spotting a clear shot, Erhi loosened her arrow. It thudded into the Khwarezmid's skull with a wet crunch. The man's neck snapped to one side, then his body crumpled underneath him and he keeled over into the snow. Erhi's heart stoppered in her throat. This was her first kill, the first time she had taken the life of another human being. She turned over her hand. The hand of a killer. It looked just the same as it had always done. Her middle and index fingers were calloused from hours of archery practice. Except this time she hadn't shot a dear or a target stuffed with straw. This time her arrow had sent a soul on its way to the next life.

The boy was hyperventilating. He kept looking from the corpse to Erhi, then patting his neck to make sure that he really was alive. As Erhi walked towards him, the boy scrambled backwards and held his hands protectively in front of his face. When she checked to make sure that the Khwarezmid was dead, the boy retched into the snow. Erhi thanked Tengri that she had the good fortune to become a Mongol rather than be raised as Chinese. The boy wiped his mouth with a grimace then frantically cast around himself, turning this way and that. Erhi realised that the strange portal was no longer floating above the ground. At some point during the fight with the Khwarezmid the portal must have disappeared. The boy cried out in despair.

"Your tears won't stop the sun from rising" said Erhi, more tenderly than she had intended.

The boy looked at her in surprise and wiped away his tears.

"You speak Chinese" said the boy uncertainly, as if he was having to think very carefully about his words before he spoke them.

"Better than you" replied Erhi, offering him a hand.

He accepted it and she raised him to his feet.

"Where are we?" asked the boy.

"On the borders of the Khwarezmid Empire, a few days march from Samarkand" said Erhi.

She whistled for Sabar and the horse obediently trotted towards her. Reaching into her saddle bag, she pulled out a short ball of rope and begun untying it.

"What's a boy from Zhongdu doing all the way out here?" asked Erhi.

"Zhongdu....oh you mean Beijing" said the boy, scratching his head.

"Hm, must have changed name since I was last there" said Erhi, measuring out the rope before cutting it with her knife

"Khwarezmid, Zhongdu...wait, wait, what year are we in?" asked the boy.

"Depends on who you ask. Turks? Christians? Jurchen-ji? Han?" said Erhi.

The boy started to hyperventilate again.

"Hands" commanded Erhi.

Without asking why the boy thrust his hands out in front of him. Good, thought Erhi, she wouldn't have to train him to be obedient. She bound the boy's hands with her rope than tied him to Sabar's saddle.

"Wait, what are you doing?" asked the boy.

"You're my prisoner" replied Erhi, mounting Sabar.

"Prisoner?" stuttered the boy.

"Yes, or would you prefer me to leave you out here as wolf bait?" replied Erhi.

"The portal...." said the boy, trailing off.

"I was hoping you could explain what that was about" said Erhi, pointing to the spot where the portal had been.

The boy merely shook his head.

"Well, you'll have plenty of time to think of an answer between here and Samarkand" said Erhi.

"Samarkand, what's in Samarkand?" asked the boy.

"For a prisoner, you ask an awful lot of questions" replied Erhi, urging Sabar into a trot.

The boy from Zhongdu struggled to keep up, tripping and sliding in the snow. He called out and tried to get her attention, but she ignored him. She had discovered a strange portal, taken a man's life, and captured a prisoner. She didn't quite know what to make of this turn of events. Far from providing answers, her nocturnal expedition had only prompted more questions. Yet she realised that she had done well to keep the boy out of Muunokhoi's clutches. Erhi was intelligent enough to know that wars weren't won through brute strength alone. Knowledge was power, and she could sense that this boy knew more than he was letting on. She would coax it out of him one way or another, of that she was sure. And when she did, she would have an advantage over everyone else, an advantage that she could offer to the Great Khan.

Wrapped up in her own thoughts, Erhi failed to notice a pure white butterfly fluttering above her head. If she had paid close attention then she would have observed the butterfly's wings twitch in a regular and unnatural manner. If she had possessed a microscope, a device that would not be invented for at least another four hundred years, then she would have uncovered an extremely fine thread, invisible to the naked eye, that ran from the tail of the butterfly to an area of thin air previously occupied by the portal. And if Erhi had focused on that precise spot without blinking she might just have spotted a minuscule purple circle, no bigger than pin prick, pulsating in the dark of the night.