"Why?"

"Why do you think?" Tris said crossly.

Zaq shrugged, then wiped his eyes with the back of his hand. "I don't know."

"Because I can't kill you if you're sitting down."

"Is that in the rules?"

"Well," said Tris, somewhat reluctantly. "It's in mine."

"Then I'm going to stay right here," said Zaq. "I mean, what would you do?"

Tris frowned. "You can't sit there forever," she protested.

"Maybe," said Zaq. "Maybe not."

In Tris's opinion the Emperor wasn't giving her the attention she deserved. She had a firm idea of how this should go and the Chuang Tzu begging for his life, expressing disbelief or at the very least demanding her reasons came high on that list.

"You know," Zaq muttered after a while, "I probably could... I mean, I don't really eat and sleep scares me." He was ticking the points off on his fingers as he went. "My muscles retain their tone whether or not I exercise. I don't know if I can actually control my waste functions but it seems possible. After all, I can control everything else.

"You should try dangling your feet in the stream," he added, when Tris just stared at him. "It might help the blisters."

"What's with the butterflies?" Tris asked eventually. Once curiosity finally overcame her irritation, it seemed an obvious enough question.

Zaq looked up from his scroll. There was ink on his fingers and his brush had splayed at the bristles where he'd been pressing too hard. His ink stone was broken in three and he'd taken to grinding one of the broken ends directly into a saucer of water. Tris was sure that wasn't how it was meant to be done, but then what did she know?

"Try one," he suggested.

And then Zaq went back to his scroll, alternating perfect circles with sketches of crude flying machines which hovered around a small hill town.

"Go on," he said a moment later. "Here. I'll show you how." Reaching out, Zaq held his hand absolutely still until a butterfly skimmed across the grass towards him.

"Watch," Zaq said.

And as Tris watched, the flicker of purple stamped on the Chuang Tzu's outstretched fingers, the man blinked and the butterfly fell dead, twirling to the ground like a fallen leaf.

"You try it."

Tris held out her hand to a butterfly and across the 2023 worlds 148 billion people sucked in their breath as Tris's body arched backwards and she hit the ground at Zaq's feet.

"That was stupid," he said.

Flames licked up both sides of the Changlang, a 2572-foot corridor built along the northern shore of a lake which bordered the Emperor's Summer Gardens outside the Forbidden City.

Only a few of the famous paintings lining its walls looked likely to survive the inferno now sweeping the wooden corridor's entire length. Tris's calling card.

Zaq hated it when people wouldn't stay dead.

"This is between me and her," Zaq said. Although he said this to himself since the Librarian was no longer talking to him.

It was muddling and strange and more frightening than he'd expected and Zaq wasn't quite sure why he was still there. If America joined Beijing, the Loyal Prince would no longer be solely Chinese. Most probably it would not even be called the Loyal Prince. Someone else would discover the 2023 worlds. There'd be no first Chuang Tzu, never mind a fifty-third... He'd rewritten history and changed everything.

So why wasn't everything changed?

Unless, of course, the man he needed to kill had not been killed. The more Zaq thought about this the more certain he became that this was what had happened.

He was trapped here, waiting for the American Emperor to die. And his own assassin was out there somewhere. No one else could have fired the Changlang and few would want to, fewer still would dare and none but the girl could have made it this far.

He blamed the Library.

The plateau should have stopped her, as it had a thousand before. And if not the plateau then the ice bridge. She'd got past both, which was unknown, and survived the stamp of a butterfly when none but the reincarnated could do that and live.

All 2023 worlds knew this and so did Zaq, because he'd patched himself into a feed. So now he watched himself staring into space, talking to nothing and sitting on the step of a pagoda while the Dragon Throne sat empty behind him.

There was little need for her to burn the buildings of the Summer Gardens. All of the doors had been left unlocked and the shutters open. The guards who might have stopped her had been absent since Zaq dismissed them months before. But she had burnt the Changlang anyway, stalking the length of its corridor with her head high, a blade stuck in her makeshift belt and her face grim. The only incongruous thing about the figure who swept through in a storm of fire had been her hands. She'd dragged them across the walls and paintings like a child rattling her stick against a fence.

And everywhere Tris's fingers had touched flames sparked.

Zaq looked pitiful sitting on those steps. A tearful young man in a dirty blue cloak and tunic, his chin in his hands and his attention focused, when it focused at all, on the burning line of the Changlang.

He wanted to be braver. Most of all, he wanted to be born someone else, someone completely different. A person the girl didn't want to kill.

"I'm going to find her," said Zaq.

A hundred and forty-eight billion people wondered if this was a good idea.

"And turn off the feed," Zaq added, pushing himself to his feet.

Silence greeted this order.

"Do it."

"You'll cause chaos." The order had been shocking enough to make the Librarian reappear. So now he stared from a puddle. As unhappy to be talking to Zaq as Zaq was to listen.

Walking to the edge of his terrace, Zaq stared down the wooded slopes of Wanshou Shan to a flickering wall of flame that had once been the greatest collection of classical paintings ever gathered into a single building.

"It's chaos already," he said.

Zaq found her at one end of a wooden pavilion in the Summer Gardens, kneeling with her back to him. She seemed be trying to crack open a small wooden chest. On the wall in front of her was a carved and gilded phoenix.

Tris had changed into a yellow silk jacket with a dragon embroidered across the back in white-gold thread. On her head was balanced a simple black hat that looked like an upturned bowl with the bottom cut out.

The sword was stuck through her belt.

Flames licked against one window and the sky outside danced with embers that flickered and spun in the night wind. The Changlang had burnt easily, being old, fragile and made mostly from cedar, and sparks from that fire had danced and then fallen onto a nearby roof.

A thousand golden butterflies rose in the night sky and threatened the roofs on which they landed. Zaq half expected the Library to fill the sky with clouds and batter the fires into submission but the night stayed almost clear and almost dark, with that silver tinge which came from the sun reflecting on distant worlds.

The room in which Tris knelt stank of smoke, charring shutters and a petrochemical reek which was oil-based paint bubbling beneath early tongues of flame. It was a complex smell, heavy with hydrocarbon. And though Zaq would have liked to stay to savour its richness, he realized this was probably unwise.

"So," Zaq said, "what are you looking for?"

"You..."

Tris scrambled to her feet so fast she almost tripped. Only to realize that a dozen paces still separated her from the Emperor and anyway he was unarmed. So she drew her own blade and stepped away from the sandalwood box.

"Nothing," said Tris.

You must be searching for something, Zaq almost said, then shrugged his reply away. Why would she tell him anyway?