Obaday and Skool could tell Zanna was upset. Obaday offered to read to her from his jacket. “Although,” he added doubtfully, eyeing his lapels, “I confess this story isn’t quite the alpine romance I was expecting…” When she declined his offer, he opened his bag and handed Zanna and Deeba what looked like two tiles and cement. They stared at them dubiously, but they were both starving, and the strange sandwiches had a surprising— and surprisingly enticing— aroma.

They bit experimentally. The tiles tasted like crusty bread— the cement like cream cheese.

Below them was the Smeath, the great river of UnLondon, drawing an amazingly straight line across the abcity. A few spirals, curlicues, and straight lines— tributaries and canals— poked off from it in various directions, into the streets. Bridges crossed it, some familiar in shape, some not, some static, some moving.

“Look at that!” Deeba cried out. Far off, there was a bridge like two huge crocodile heads, snout-to-snout.

Deeba started humming a tune, and Zanna snorted with laughter and joined in: it was the theme song to the program EastEnders, which started with an aerial shot of the Thames.

“Dum dum dum dum dum, deee dum,” they sang, looking down at the water. The passengers looked at them as if they were mad.

A few birds and intelligent-seeming clouds examined the bus curiously. “Here comes a highfish,” said Jones, and the girls jerked back in horror at the approaching jackknifing body, its ferocious teeth and unmistakable shark fin. It glided with a faint burring sound. Where its ocean cousins’ side fins were, it grew dragonfly wings.

Jones leaned out and banged the side of the bus. “Get out of it, you dustbin!” he shouted, and the big fish darted off in alarm.

“What is that ?” said Zanna. They were approaching a truly enormous wheel. Its base dipped into the river, and its highest point arced hundreds of meters up, almost to the bus.

“The UnLondon-I,” Jones said. “It’s what gave them the idea for that big wheel in London. I saw some photos. Ideas seep both ways, you know. Like clothes— Londoners copy so many UnLondon fashions, and for some reason they always seem to make them uniforms. And the I? Well, if an abnaut didn’t actually come here and see it, then some dream of it floated from here into their heads. But what’s the point making it a damn fool thing for spinning people round and round? The UnLondon-I has a purpose.”

He pointed. What had looked at first like compartments were scoops, pushed around by the river. The UnLondon-I was a waterwheel.

“The dynamos attached to that keep a lot of things going,” Jones said. Above the wheel was the ring of sunshine. The two circles echoed each other.

“Some people say,” Jones said, “that the bit missing from the middle of the UnSun was what became the sun of London. That what lights your days got plucked out of what lights ours.”

Zanna held out her thumb. The hole in the UnSun’s center was about the same size as the sun from their usual life.

“Every morning it rises in a different place,” Jones said.

The UnSun glowed. Strange shapes flew around it, the air-dwellers of UnLondon. There were chimneys all over the abcity, but very few were venting smoke. A dark shape approached over the miles of sky.

“Conductor Jones,” Zanna said, and pointed at the incoming smudge. “What’s that?”

He pulled a telescope from his pocket and stared into it for a long time.

“It’s a grossbottle,” he muttered. “But why’s it so high? It should be down feeding on dead buildings…” Suddenly he yanked the telescope to its full extent. “Uh-oh,” he said. “Trouble.”

The shape was close enough to see clearly now. It raced towards them. It was at least the size of the bus. All the passengers were crowding the windows, alerted by the drone of its approach.

The grossbottle was a fly.

“It would never normally come for us,” Jones said. “But look— see the howdah?”

On the creature’s huge thorax was a platform full of figures. “It’s being driven,” he said. “Airwaymen. Thieves. But I don’t understand. They go for solo balloons, maybe deep-sky trawlers. They know buses are defended. Why risk it?

“Time to go to work.” He unhooked his bow from the cabinet. “Rosa,” he shouted. “Aerobatics!”

The grossbottle fly careered towards them. The airwaymen whipped it, prodded it with barbs, and readied weapons. Obaday and Skool were staring at it, aghast.

Deeba saw motion above her again. She nudged Zanna. There were two little moving presences, but they weren’t crabs. They were hands, poking through the ceiling, fingers scuttling, emerging from the metal— then they were gone.

Someone stood. Deeba looked down into the face of the bearded man. Alone among the passengers, he did not look afraid as the grossbottle came closer. He met Deeba’s eyes. Through a gap in the toga, she saw familiar paint stains.

Before she could speak he had leapt up and grabbed…Zanna.

“Help!” Zanna shouted. “Deebs! Obaday! Skool! Jones!”

Deeba was helplessly pointing at the man, and up at the ceiling.

“He heard us in the market!” Deeba said. “He must’ve run to Manifest Station. He was waiting for us. He sent a message to them.” She pointed in the direction of the oncoming fly. “And there’s someone upstairs, there is —”

“Shut it!” The man gripped Zanna by the neck. She struggled, but he was too strong. He held her in front of him like a shield.

Curdle launched itself at him, but he kicked the little carton away. The passengers huddled terrified. The man tightened his grip on Zanna.

“Nobody move!” he said.