A moment or two later he changed his mind.

"Oh, come on then."

Holding out his hand, Zaq watched the butterfly make its short journey from mulberry leaf to Zaq's wrist, dying in a tiny flash of electricity.

"Back yourself up." The order was stark, except it wasn't an order. The Council of Ambassadors couldn't give orders, they could merely make suggestions. Ones that the Emperor was entirely free to ignore. Of all the suggestions they'd relayed to the Librarian, this was certainly the shortest.

"No," said Zaq, "I don't think so."

Backing himself up meant returning to Baohe Dian, the Hall of Preserving Harmony, to be examined by the imperial doctors. After which he would sign orders making General Ch'ao Kai regent for the eight minutes it would take Zaq to be read, found adequate and recorded. Maybe the Library had a host already prepared, a second Zaq blissfully sleeping away his non-life in a glass tank somewhere.

Zaq had in mind the pods originally found on the SZ Loyal Prince, which he'd visited. This was rare among emperors, who mostly sat quietly in the Butterfly Garden or retired to the silence of the Library to practice calligraphy, draw endless misty mountains or note down their carefully composed words of wisdom.

Of course, for them the SZ Loyal Prince was historical abstraction, not somewhere they'd called home for the first seven years of their lives. Zaq was aware that as Chuang Tzu he had been less than impressive. Rapture still existed and the 2023 worlds were healthy, true enough, their peoples no more bored or less happy than under the putative rule of any of the other, earlier emperors.

Only he'd intended to be so much more and would have been if he'd had the courage of the assassin who struggled so hard through the snow and storms Zaq sent against her. This small, cropped-haired figure wrapped in a cheap jacket and torn trousers, who talked to the air, slept oblivious and alone on a storm-tossed bridge and rose the next morning, equally oblivious as to why the storm now stilled. Zaq was exhausted from trying to live up to the assassin's expectations.

"Oh well," he said, climbing to his feet. Turning, Zaq hurled the peach he held against the grey up-stroke of a willow. It was a perfect shot and the fruit burst as it exploded against pale bark, staining the willow's trunk with a smear of darkness.

Zaq would have given anything for the peach to contain a maggot, to be bruised or rotten at the stone, but that would never happen. Perfection was required for the Emperor, even in the Butterfly Garden, and the Library was there to ensure perfection was what he got.

The maggot, the bruising and the rot were inside Zaq's head. He didn't think anyone had much doubt about that.

"Go back," Tris suggested.

The words popped out of her mouth in that way words sometimes do. A fleeting thought suddenly translated into speech with no filter betwen original thought and open mouth.

"Go...?" Luca looked amused, tired and almost dead on his feet, but very definitely amused. "Go where?" he asked.

"Home?" Tris didn't intend a question, that just happened to be the way it inflected. "You should go back," she added, more decisively. "You're exhausted. I can manage from here."

"Manage?" His smile became a sad grin. "Of course you can manage," Luca said. "I'm not here to help you."

"You're not?" demanded Tris.

Luca shook his head. "You're helping me," he said. And in that moment he sounded like an adult talking to a very small child. An intelligent, well-loved child, but a child all the same.

Moving Tris gently to one side, Luca stepped off the bridge and onto solid rock. "There's no way I could have escaped the village before you arrived."

"Why not?"

Luca's look was kind, if slightly exasperated. The look of someone who really didn't quite know where to begin. In the end, all Luca said was, "Rapture wouldn't let me."

"Why not?"

"The storms, the plateau, the ravine, the bridge... They're linked, you know." He glanced at her. "You do know that, don't you? That everything on Rapture is tied to everything else and all of it tied to the happiness of the Emperor."

"Really?" Tris said.

"At all levels," said Luca. It was obvious that this was news to Tris. "Didn't anyone ever explain quantum interdependence?"

Helping Tris onto the rock, Luca brushed snow from her blue jacket and peeled frost from her eyebrows. He did this without thinking, the way a father might do it for a daughter and Luca knew, at a theoretical level, that treating Tris this way made for problems because he'd already bedded her, creating the template for an entirely different if less complex relationship.

Luca knew this only at a theoretical level because he'd met very few people from the 2023 worlds. In fact, to be honest, the only person with whom he'd talked closely was Tris and he questioned whether she really represented that culture at all.

The girl certainly didn't fit his image of a hyper-educated, sexually sophisticated, slightly blasé member of the richest society yet existing, which was how the Always Knowledgeable and Correct Empire of the 2023 worlds sold itself, mostly to itself.

"Which world do you come from?" Luca was sure he'd asked Tris this question before and had memories of not understanding her answer.

A second snow-covered plateau extended for at least a day and maybe longer beyond the bridge. Because there were few hills and no actual valleys, the snow had spread evenly across the undulating surface and the flakes were so dry they barely stuck to Tris's and Luca's shoes, although this dryness meant the plateau's surface was forever sifted by the wind.

And yet even the wind seemed to be in their favour, shifting to the west to blow gently against their backs and coax them on their way.

"Something's changed," said Tris.

"No," Luca said. "Everything's changed. Take a look around you."

The sun was beating down on the snow and a billion diamonds of light flickered in its brightness. The whole thing looking like nothing so much as a crust of solidified foam.

"This is good, right?" Tris asked.

"Well." The Baron shrugged. "It's certainly different."

In the end the plateau didn't so much finish as fall away into a slope that got steeper and steeper until suddenly it stopped being a slope. This happened at a point where the crust over which they walked slipped over the horizon and vanished altogether from sight.

"Walk backwards," Luca suggested. "You'll find it easier if you know where you've come from." Gripping his sticks, Luca strode to the start of the steepness, turned to face Tris and then stepped back, jamming both thorn sticks deep into the snow. He would like to believe that what he hit was earth, but chances were it was compacted snow, ice or bare rock because the ends of his sticks slid slightly.

"And dig deep," he added.

Tris did as she was told, turning as Luca had done and stepping back, feeling for a foothold that seemed further away than it ought to be. Her sticks slipped a little and then locked into place.

"If you feel yourself slip," said Luca, "ram both sticks into the snow and keep hold." The twine from his trap was gone, lost along the way, and this was irritating because he'd have liked Tris's sticks to be lashed to her wrists and he lacked the strength to tear fresh strips from his cloak. Tris had almost no idea how tired Luca was and he hoped to keep it that way.

Afternoon slid into evening, the high cirrus having cleared to reveal the silver shimmer of a sky filled with worlds around the distant sun, as if some insane mosaicist had decorated the inside of a globe with tiny tesserae and then not bothered to fill in between the tiles.