‘Look out!’ he called hastily as he stopped his sudden slide with a slap on the glass.

Suzy popped the diamond in her mouth and slapped her other hand down just in time. Then she resumed her work with the gem. The diamond didn’t actually cut through the glass, but it scored it enough so a solid hit would snap off the pinnacle of the pyramid, allowing them to climb inside to the weathervane atop the tower.

‘They’re going to fire the steam-cannon,’ said Soot anxiously. ‘Hurry! Hurry!’

Arthur looked down. The bronze barrel was being elevated to target the top of the pyramid, Overseers frantically turning wheels and gears. Long wafts of steam were escaping from the end of the barrel, and the steam engine was blowing a steady stream of thick black smoke.

‘Only a bit more to cut,’ Suzy said to Arthur. ‘You’d better hit it, rather than me. It will probably need the power of the First Key. Take the tube from my belt.’

Arthur reached over and slid out the copper tube. Suzy finished the deeply scored line she’d drawn right around the pyramid, about four feet down from its point.

‘Hit it!’

Arthur swung hard. The copper tube bounced off, jarring his hand. But there had been a definite cracking sound and his hands were hot. He swung again, and this time the cracking sound was so loud he had no doubt that the point of the pyramid had broken all along the diamond-cut line.

Together, Arthur and Suzy pushed at the top part of the pyramid. It resisted for a moment, then snapped off. The top three feet of the pyramid toppled over and fell down the other side, leaving a nice square access hole directly above the weathervane.

Arthur’s stickits changed and he slipped back a few feet before he could slap his other hand down. Suzy quickly tested the edge of the inch-thick glass.

‘It’s not sharp,’ she said, and climbed up and inside the pyramid, her feet tapping the east-west crossbars of the weathervane to make sure they’d take her weight.

Suzy’s right hand stuck to the glass as she lowered herself down. She pulled at it, then quickly said, ‘Stickit fingers, my thanks to you, your work is done, till called anew. ’

‘That’s the spell, Arthur,’ she added, her voice suddenly fading as her head dipped below the lip of the hole. She waved at Arthur through the glass, and he faintly heard her say, ‘Come on!’

Before he could move, Soot swarmed past him, dived into the hole, and slid down the weathervane on the opposite side from Suzy. It continued to the roof of the tower and disappeared from Arthur’s sight.

A second later, the first blast of long-range steam screamed up the side of the pyramid, clouding the glass as it came.

Arthur swung his legs into the hole and Suzy helped place his feet on the crossbars of the weathervane. He crouched down as low as he could, so he was almost entirely inside the pyramid. Almost - but his right hand was stuck outside, firmly glued by the stickit fingers.

Arthur opened his mouth to speak the unsticking spell, but he only got the first word out before the steam hit. Most of it hurtled above his head, but some spilled back down inside the pyramid. Arthur ducked down even more as it scalded his ears and the back of his neck. It hurt, but he’d only suffered the cooler edges of the blast.

Except for his right hand. That must have been right in the middle of the superheated stream of steam. But it didn’t hurt. Arthur didn’t look for a moment, imagining that he couldn’t feel the pain because it was so intense, and all that was left were the bones. Then he discovered that his right hand was clenched against his chest and his left hand was stuck to the weathervane. The stickits must have swapped an instant before the steam hit, and Arthur had instinctively snatched his hand in just in time.

Arthur sighed a very deep sigh of relief and recited the spell. Immediately, the stickits on his left hand quieted down and stopped wriggling.

‘This is hinged,’ said Suzy, who had climbed down to the roof and was examining the base of the weathervane. The whole thing was about six feet high and made of cast iron, so it would be very heavy. Arthur tapped the cold iron beak of the cockerel and wondered how they were supposed to lift it and get inside the tower, as Dame Primus had suggested. Even if it was hinged.

‘There must be a catch somewhere,’ added Suzy. ‘A lock or lever . . . ah –’

She pressed a hidden button. There was a loud metallic zing! and Arthur was flung violently into the air. He smacked down onto the roof of the tower and rolled down the tiles to the gutter. His legs went over and he scrabbled desperately to get a grip, his fingers no longer sticky.

At the last second, he grasped the gutter, leaving his legs dangling over the side of the tower. Arthur tried to breathe a sigh of even temporary relief, but he couldn’t get a breath.

Then there was a rattle on the tiles and Suzy’s anxious face appeared, looking down at him and the ground, several hundred feet below.

‘Sorry!’ said Suzy. ‘It was spring-loaded . . .’

‘Help me up!’ whispered Arthur. His breath was coming back. Once again he was grateful to be in the House. If he’d had the wind knocked out of him like that back home, he would’ve had an asthma attack for sure.

‘Swing your feet back, I mean behind you,’ said Suzy. ‘The pyramid wall is only a few feet away. Push against it and I’ll pull you over.’

It took several minutes to get Arthur onto the roof. He lay on his back for a few minutes, panting, then wearily sat up.

Suzy was looking into the hatchway under the weathervane, which now hung at a right angle to the tower. Arthur slowly climbed up next to her, thankful that the pitch of the roof was not too steep.

‘Bigger inside than out,’ muttered Suzy, still looking inside. ‘And that Soot thing has scarpered.’

Arthur looked through the hatch. Even with Suzy’s comment, he still expected to see something like a round tower room.

But the inside of the tower bore no relationship to the outside. It wasn’t even round. It was rectangular and vast. It reminded Arthur of a nineteenth-century prison he’d visited on a school excursion. Large and gloomy, it had an open internal courtyard with many levels of cells built into the brick walls on each side, each traced by a cast-iron walkway.

The prison Arthur had visited had six levels, with a hundred cells or so on each side. The Grim’s treasure prison had at least fifty levels, and the main courtyard was a mile long, maybe more. It was hard to tell, because the only light came from flickering oil lanterns – or imitations of lanterns – that were placed in wall brackets between every fourth cell. There had to be at least a thousand cells on every level, Arthur calculated, which meant there were more than fifty thousand rooms!

‘It looks like a prison,’ said Arthur. ‘I mean, it looks almost exactly like one I visited back home. Only much, much bigger.’

‘That’s what Grim Tuesday does,’ said Suzy. ‘Copies stuff.We’d better start looking for theWill.’

‘Start!’ exclaimed Arthur. He looked down at the iron ladder that led to the top-level walkway, and the cells stretching to the left and right – a seemingly endless row of riveted cast-iron doors. ‘Where do we start?’

‘Depends what you’re looking for,’ said Soot, unexpectedly appearing out of the gloom at the top of the ladder. ‘Did I hear you mention . . . theWill?’

‘Do you know where it is?’ asked Arthur eagerly, before he remembered he didn’t want their real business known to Soot.

Soot reared up and flexed, showing its nasty sucker underside again. Arthur leaned back from it, struck by the notion that it had got bigger somehow. It certainly looked about half again as big.

‘TheWill of the Architect?’ asked Soot. ‘That part of it entrusted to Grim Tuesday?’

‘Yes,’ said Arthur. Soot’s voice had dropped in pitch as well. It sounded more menacing, less eager to please than it had before. As if Arthur and Suzy were less useful to it now that it had got into the Treasure Tower.

‘I don’t know where it is exactly,’ replied Soot. Its silver eyes weighed up Suzy, who had hefted her copper tube, and it backed down the ladder. ‘But I know where it must be. Follow me.’

Soot slithered and popped down the ladder and onto the top walkway. It didn’t look back to see if they were following.

‘It’s got bigger,’ whispered Suzy. ‘Like a Nithling that’s sucked the life out of someone.’

Arthur nodded and bit his lip.

‘We have to follow it,’ he said finally. ‘There are too many cells to check every one. Particularly since Grim Tuesday must know we’re in here by now.’

‘What if it’s leading us into a trap?’

‘I still think we have to risk it.’

‘I s’pose so,’ said Suzy. ‘But keep your eye out for an architectural sword, or a light-axe, or something. If it gets any bigger, we’ll need a better weapon than this copper pipe.’

Arthur nodded and led the way down the ladder. His leg still felt weird and it felt weirder still when he finally stood up straight on the walkway. He took a few steps, stopped, then felt both his knees, his forehead wrinkled in puzzlement.

‘What is it?’

‘My leg . . . the one I broke,’ Arthur said hesitantly. ‘It’s got shorter. It’s an inch shorter than the other one!’

He bent down and felt his legs again. His clogs were long gone, fallen off into the Pit. He was standing in his socks, and there could be no doubt. He’d magically healed his broken bone, but he’d done it wrong. Not only was his leg a bit twisted, it was definitely shorter.

‘It is shorter,’ confirmed Suzy in a conversational tone. ‘Come on, that Soot is going down those stairs to the next level.’

‘You don’t get it!’ cried Arthur. ‘My leg is shorter!’

He coughed as he said it, his breath catching. He could feel his lungs tightening, but it couldn’t be asthma. Not here in the House. It was shock, or a panic attack, or something. It was bad enough having asthma and not being able to do everything. Now he was lame as well. Everything would be worse –

Arthur stopped himself.

I am not going to think about this now. I have to find Part Two of the Will, defeat Grim Tuesday, and get back in time to save the house and all our money and stop anything worse from happening. So one leg is a bit shorter? That’s better than it being broken, isn’t it?

‘Come on!’ repeated Suzy. She started off, and Arthur followed, lurching as he got used to his shorter leg.

They had to run to catch Soot, as the thing undulated down a set of iron steps to the next level, along it for a hundred yards or so, and then continued straight on down to the level below that.

Even in their socks, Arthur’s and Suzy’s footsteps rang on the metal walkway, the sound echoing through the vast open space in the middle.

‘If there are guards here, they’ll know where we are,’ said Arthur anxiously. His voice echoed out into the central courtyard, carrying even more than their footsteps.

‘There are no guards,’ called Soot. It had stopped outside a cell door that looked the same as all the others. ‘Grim Tuesday allows no one but himself to enter the Treasure Tower. Not even the Grotesques are allowed in here. But at last I am where I should have always been – with all the lovely treasure!’

Arthur and Suzy grimaced and stepped back as thick, translucent saliva dribbled out of Soot’s mouth and dripped down through the cast-iron mesh of the walkway.

‘Is theWill inside that cell?’ asked Arthur. It seemed a bit too straightforward for someone like Grim Tuesday to keep the Will here, even if no one but himself – or his former eyebrow – could know which of the five thousand rooms to look for.

‘There should be a way to the Will inside,’ said Soot, its drool bubbling as it spoke. ‘But here I must leave you. Other, more easily digestible treasures await me!’

It leaped backwards and over the railing as Suzy rushed forward to hit it with the pipe. She and Arthur rushed to look over the side, only to see Soot several levels down, clinging to the side of the walkway there. With a loud popping, it slithered underneath the walkway and was gone from sight.

‘Good riddance,’ said Arthur. ‘I suppose.’

‘If it’s led us to the right door,’ said Suzy. She looked it over, then tried to slide back the inch-thick bolt. It didn’t budge, even when she pulled with both hands and pushed with her feet against the rim of the door.

‘Stuck, or magically locked,’ she said. ‘Not even a padlock to pick.’

Arthur examined the bolt. It actually looked welded in place, with thick strands of metal between the bolt and the loops. As he touched it, Arthur’s hand felt suddenly hot. Flakes of rust fell to the floor, the bolt rattled, and Arthur easily drew it back.

Suzy whistled in admiration.

‘That’s a good trick.Wish I could do the same thing to Dame Primus’s biscuit pantry.’

Arthur pushed the door open and stepped inside.

FOURTEEN

ARTHUR STEPPED INTO another room that was bigger inside than out. This was no tiny cell, but a room about the size of the big family room in Arthur’s house – the house that they would lose if Arthur couldn’t stop the Grotesques.

Apart from the overall size, this room had nothing in common with Arthur’s family room. For a start, it looked more like a ship’s cabin than a room. The brick walls of the prison were gone, replaced by wooden planking, sealed with tar that had dripped in numerous places. The ceiling and the floor were planked too, and everything creaked a little as Arthur walked farther in. The only light came from a lamp that swung on a chain from the ceiling, making the shadows shift and sway.