‘I guess we’re good to go,’ said Arthur. He looked across at Suzy and raised his cheese. She raised her lump back, as if making a toast.

‘Let’s eat!’ said Arthur, and he bit his cheese.

It wasn’t very tasty cheese. Arthur swallowed another huge mouthful and felt suddenly quite sick, the cabin spinning as it never had before. He started to say something about seasickness, and the change in the swell, but stopped. He was dizzy because he was shrinking and his eyes were moving in his head. His field of vision was changing – the things in front of him were harder to see, but he could see far more to the sides. The cabin was brighter than it had been too.

‘Excellent!’ exclaimed Scamandros. A tattooed torrent of Rats ran out from under his neckcloth and up the side of his face. ‘It works.’

‘Yes,’ said Arthur. He looked down at his odd, foreshortened arms and saw they ended in pink paws. ‘I’m a Raised Rat.’

His voice was higher-pitched and husky. He raised one paw to check that the bag with the Key and Elephant was still there. It felt much heavier than it had before, but it was securely fastened.

Arthur slowly began to get dressed, his paws fumbling till he got used to them, and to his different vision. He’d just finished doing up his trouser buttons when Lieutenant Finewhisker knocked and entered the cabin without waiting for a reply. He saluted Arthur, who inclined his snout in greeting.

‘Ready for the Nebuchadnezzar, Lord Arthur?’ Finewhisker asked.

‘Yes,’ Arthur replied.

‘Very nice clothes you have on, if I may say so,’ said Finewhisker cheerily. ‘Excellent taste. Now, a twist here, a twist on the other side . . .’

He deftly removed the wire cage that held the cork in place, and then gently turned the huge cork, easing it out. It made a screeching fingernails-on-the-blackboard noise as it slowly revolved out, and then a surprisingly small pop as it came free and Finewhisker staggered back with it in his arms.

A thin waft of smoke billowed out the neck of the bottle – black, choking coal smoke.

‘You need to jump straight through the neck,’ Finewhisker instructed. ‘A good strong jump with your paws forward. Avoid touching the glass if you can.’

‘Thank you, Finewhisker,’ said Arthur. ‘Thank you too, Doctor Scamandros. I will see you at the Citadel, I hope.’

‘Good luck, Lord Arthur,’ said the sorcerer. He bowed and added, ‘The spell will last a few hours, I should think.’

‘Come on, Arthur!’ said Suzy. She hopped over to the bottle and tensed, ready to jump at the neck. ‘Last one in is a stinking ra . . . um . . . rabbit.’

Arthur pulled her back by the scruff of her neck.

‘Not this time, Suzy,’ he said. ‘I go first.’

Suzy wriggled but didn’t really resist as he moved her aside. Even as a Raised Rat, he was unnaturally strong, though it didn’t occur to him that he shouldn’t be able to pick up someone who weighed as much as he did, using only a paw.

With Suzy out of the way, Arthur took a few practice hops across the cabin. Then he stretched his paws and backed up to stand in the open cabin doorway, facing the open neck of the Simultaneous Nebuchadnezzar. Smoke was still wafting out of it, and the interior was dark and cloudy.

Bravery and stupidity can be quite closely related, Arthur thought. I wonder what this is going to be . . .

He bent his legs, rushed forward, and dived straight at the open neck of the bottle.

He was in midair when a terrible last-minute thought slipped into his head:

What if the Raised Rats are lying? What if this bottle takes me somewhere entirely unexpected?

NINE

ARTHUR HAD EXPECTED to land inside the huge green glass bottle, at least for a few seconds before he was transferred, but instead he found himself diving out of the neck of a completely different Nebuchadnezzar, one made of sparkling blue glass. He landed heavily on a floor made of lozenge-patterned iron mesh, which hurt and left an imprint of itself on his fur.

Arthur rolled to a stop and immediately got up. He hardly had a moment to look around before a Raised Rat he only barely recognised as Suzy crashed into him and they both went sprawling on the iron floor again. They were disentangling themselves when a harsh, low voice spoke.

‘Quickly now! Help me move the bottle! They’ll be on to us in a minute or two.’

Arthur jumped up and looked around. The blue Nebuchadnezzar was on a lashed-together wooden trolley with uneven wheels, and pushing it was the strangest, ugliest Piper’s child that Arthur had ever seen. He wore a black cloak and a broad-brimmed hat with a feather, but even under the shadow of the brim, Arthur could see that the boy had a lumpy face and a ridiculously large nose.

The Nebuchadnezzar, Arthur, Suzy and the ugly Piper’s child were all on a broad metal walkway suspended from the ceiling by bronze rods every few yards. Though it was twelve feet wide, it had no rails, and was wreathed in smoke and steam.

Arthur gingerly peered over the edge. There was nothing beneath the walkway, no sign of solid ground. All he could see was a thick cloud of roiling black smoke. He could hear the whoosh, hiss and deep bass beat of big steam engines somewhere down below, but he couldn’t see any sign of them.

Then the smoke currents whorled and shifted and he caught a glimpse of the upper half of a huge bronze wheel as big as a house. It was turning very slowly, but before Arthur could see what it was connected to or what its purpose was, more smoke billowed across and obscured it again.

Closer to the walkway, a black cloud parted to reveal the end of a huge, rusted iron beam that was as long as three school buses joined together. The beam rose up through the smoke like a whale breaching, then descended into the depths with a gargling whoosh, and the industrial fog closed up again.

The metal mesh under Arthur’s feet was vibrating in time to the beat of the engines below, and the bronze supporting rods hummed at Arthur’s touch. The rods were tarnished, Arthur noted with concern, and their connection to the ceiling looked none too secure, though it was hard to see exactly how the thirty-foot-long rods were joined to the stone above. Judging by the occasional clean patches, the ceiling was a solid, pale rock, but most of it was so stained with soot that it resembled a dirty carpet of the blackest plush.

‘Hurry! Help me push!’ cried the Piper’s child. He was struggling to get the bottle moving.

Arthur cautiously ran around the right-hand side of the bottle while Suzy ran around the left. They put their shoulders to the base of the Nebuchadnezzar and heaved. The trolley creaked and rumbled forward, slowly gathering speed. It had a tendency to veer dangerously off toward the edge, so all three pushers needed to be constantly vigilant.

‘Got to get it back to the lubricant store,’ wheezed the Piper’s child. ‘Fill it up with oil again and make ourselves scarce. You’ll need disguises too.’

Arthur glanced across at the boy and did a double take. It wasn’t a Piper’s child at all under the broad-brimmed hat with the scarlet feather, but a Raised Rat wearing a papier-mâché mask painted to look like a human face. The ridiculous nose covered the Rat’s own snout.

‘Lord Arthur, I presume,’ husked the Rat. ‘Dartbristle, at your service.’

‘Good to meet you,’ said Arthur. ‘This is my friend Suzy.’

‘General Suzy Turquoise Blue if you don’t mind,’ sniffed Suzy.

‘Welcome to the Upper House, General,’ said Dartbristle. ‘Up ahead, we need to heave her around to the left. Hurry now.’

The walkway met another broader walkway at a T-intersection. Manhandling the trolley around without it – or them – falling off the edge was no easy task, but they got it turned and were able to push the Nebuchadnezzar faster once they were in the clear.

Dartbristle kept looking behind them, so Arthur looked too, but all he could see was the thick, grey smoke, with occasional eddies of thicker, blacker smoke coiling up through it. He was no longer surprised that the smoke had no effect upon him. In fact, he even quite liked the smell, though he knew that his old human lungs would have quickly failed in the toxic atmosphere.

‘What are you looking for?’ Arthur asked after they had pushed the bottle several hundred feet and there was nothing to see ahead or behind except more of the platform and more of the smoke.

‘Ratcatcher Automatons,’ said Dartbristle. ‘The sorcerers know when the Nebuchadnezzar fires up – least they know there’s serious sorcery afoot – but it takes ’em a minute or two to plot where it occurred. Since we’re under the floor, they don’t come down here themselves. They send Ratcatchers. But I reckon we might have got away fast enough. Lubricant store’s just ahead, in the bulwark rock.’

‘We’re under the floor of the Upper House?’ asked Arthur.

‘Yep.’ Dartbristle moved around to the front of the bottle and slowed it down as they came up to a sheer and apparently solid rock face of grimy yellow stone that was shot through with barely visible veins of a glowing purple metal. ‘We’re in the bulwark between the Middle and the Upper House. Saturday had a bit of the top part of it burrowed out to put in all her steam engines, chain gear, and so on. Where is that bell push?’

The Rat began pressing different protuberances of rock, but none of them moved in the slightest.

‘Curse the thing, always moving around. You’d think it was made by a practical joker!’ Dartbristle griped.

‘There’s something behind us,’ said Suzy. ‘I saw something go under the walkway.’

‘Ratcatcher!’ hissed Dartbristle. He reached under the Nebuchadnezzar and drew out three long curved knives from the trolley, handing one to Suzy and one to Arthur. ‘They’re armoured, so you need to get them in the red glowing bit right on the front of their head. I suppose it’s an eye or something like it. But watch out for its nippers. And the feelers – they’re like the tentacles of a Blackwater squid.’

He spoke quickly and unhooked the mask from his face so it dangled under his mouth, allowing him to see better. His deep black eyes moved rapidly from side to side, and his nose twitched as he tried to smell the approaching enemy. Suddenly he started forward and raised his knife.

‘Where is—’ Suzy started to say, when all of a sudden the Ratcatcher Automaton sprang out from under the walkway. Darting forward in a flash of steely plates and accompanied by a sound like the soft chink of coins in a leather purse, the twelve-foot-long, two-foot-wide, metallic praying mantis opened its huge claws and nipped at Dartbristle. At the same time, its impossibly long, razor-edged feelers whipped at Arthur and Suzy.

Dartbristle ducked under and around one set of pincers and heaved on the joint, pushing the automaton’s left claw into its right, whereupon they gripped each other tightly. Suzy jumped back from a feeler. It cut her across the chest and tried to wrap itself around her neck to cut her head off, but she blocked it with her knife and slid under the Nebuchadnezzar trolley.

Arthur instinctively parried with his knife and twisted it to trap the feeler. Then, without thinking, he grabbed it and heaved. The razor edges cut his hand, which hurt, but he also managed to pull the feeler entirely out of the Ratcatcher’s head, which caused a great fizz of sparks to jet out like a firework.

‘Get the red eye!’ shouted Dartbristle. ‘While the claws are locked!’

Arthur ran forward. The automaton’s remaining feeler whipped at his legs, but he jumped over it, leaping so high that he landed on the Ratcatcher’s back. The automaton immediately threw itself backwards, but he gripped it around its triangular head and plunged his knife deep into the red orb at the head’s centre. The little bag that held the Fifth Key knocked against the Ratcatcher’s metal overlapping metal plates as Arthur stabbed the automaton several more times, before at last it gave a high-pitched, almost electronic squeal and slowly collapsed to the walkway, its rear legs hanging over the edge.

Arthur carefully climbed down, anxious not to overbalance the defunct automaton and send both of them down into the smoky depths. As soon as the boy stood safe on his own feet, Dartbristle began to push the Ratcatcher over the side.

‘They can track these too,’ he said. ‘More come to find the remains, whenever one is slain.’

Arthur helped him push, and Suzy slid out and gave the Ratcatcher a not very helpful but certainly satisfying kick just as it tumbled over.

‘Right – I’ll get that door open,’ said Dartbristle. He looked admiringly at Arthur and added, ‘Well fought, Lord Arthur.’

‘Thanks,’ said Arthur absently. He looked at his paw and saw that it was already almost healed, the gold blood disappearing as it dried. Belatedly he remembered that Suzy had been hurt.

‘Suzy, that feeler cut you! Are you all right?’

Suzy, who had been looking over the side, turned around. Her shirt was cut through and gaped open, and there was a line of blood across her furry stomach, blood that was neither the blue of a Denizen nor entirely the red of a human, but something in between.

‘Nah, I’ve had worse,’ Suzy said dismissively. ‘If I’d ’ad my old coat on, it would never have even broken the skin. Give it a day or two to scab up and I’ll be right as rain.’

‘Found it!’ declared Dartbristle. He pushed energetically on a slight knob of rock that was at the level of his knee. His push was answered by a rumble inside the stone. Slowly, a great rock-slab door as wide as the walkway pivoted open.

‘In with the bottle,’ ordered Dartbristle. He started pushing the trolley, and Arthur quickly joined him. Suzy moved more slowly to help, and Arthur noticed she grimaced as she set her shoulder to the Nebuchadnezzar and began to push.