“This is the plan.”

The bus juddered and arced. “Rosa can’t avoid both those grossbottles. We have to get you out of here,” Jones said to Zanna.

“What about the passengers?” Zanna said.

“Don’t worry about them,” he said. “I’ll make sure they’re looked after. But the longer those things follow us, the more of a head start you’ll have.”

The toga-wearing man was gagged, blindfolded, and tied up. “We’ll get him to the Propheseers,” Jones said. “And we’ll meet you there. Okay?”

“You’re going to make us go on alone ?” Zanna said.

She and Deeba stared at each other, aghast.

“You can’t!” said Deeba. “We don’t know anything about where we’re going!”

“We don’t know where we are… ”

“We just can’t… ”

“I know,” Jones said gently. “Believe me, I wouldn’t if I had any choice. We don’t have much time. There are two gangs of skyjackers on the way, and we have to get them off your trail. They know where you’re trying to get, but we can mislead them as to how you’ll get there.”

“Please…” said Zanna.

“You’re the Shwazzy, ” he said, silencing her. “You can do this.”

“What about me?” said Deeba. “I’m not.”

“Look to your friend,” Jones told her. “Together, you’ll be okay.”

“Obaday,” Zanna said. She squeezed the unconscious man’s hand. He muttered, “I wish you could come…”

“Can you…?” said Jones to Skool, who slumped in dejection and pointed at the heavy diving boots, miming I am too slow.

“You can do this, Shwazzy,” Jones repeated.

The bus plunged. Passengers screamed. The grossbottles homed in.

“We have one go at this,” Jones said. “We’ll only lose them for a few seconds. We’ll drop you at the edge of Slaterunner territory, then lead them away. Slaterunner hunting grounds lead almost all the way to the Pons Absconditus.

“Tell them if they give you safe passage they’ll have earned the gratitude of the UnLondon conductors. Now hold on. Rosa’s going to do her stuff.”

UnLondon came so fast all Zanna and Deeba could see was a rush of colors. The aerobus hurtled down. It sped below roof-level, lurching left and right along streets. Crouched on the platform, the girls glimpsed the astonished stares of UnLondoners, saw hats yanked off heads by the bus’s passing. Rosa took them under a bridge so low that the top of the balloon scraped on its arch.

“Now, Rosa!” Jones shouted.

Instantly the bus zigzagged and, so suddenly that the shock sent them lurching forward, stopped.

“Now! Now!” hissed Jones, bundling Zanna and Deeba to the edge of the platform. Deeba held Curdle. The terrified little carton tried to burrow into her hands. The bus dangled a few feet above acres of roof, over a valley between ridges.

“Jump,” said Jones. They hesitated a second, then thought of the flies close behind them. First Zanna, then Deeba, jumped.

They landed in the bottom of the V, and the air was knocked out of them.

The bus was hovering. “Are you okay?” Jones hissed, Skool peering over his shoulder. The girls nodded. “That way to the bridge. Stay high and find Chief Badladder. Tell her I sent you. Show her the pass. Tell her I’ll owe her. Stay safe. ” He blew them a kiss, and shouted at Rosa to go.

The bus soared, something pale seemed to drop from it, and it shot away. The two grossbottles droned into view, buccaneers on their backs, and scudded in the bus’s wake.

“What was that?” said Zanna. “Did you see something…falling? From the bus?”

“I dunno,” whispered Deeba.

Wind chilled Zanna and Deeba. The noise of the flies ebbed away.

The two girls sat in the cold. Silence settled on them like damp. They shivered. They were tired and overwhelmed, and suddenly very, very alone.