The other end of the ramp joined a dusty, well-trodden road lined with white rocks that stretched to the tile border, half a mile away. On either side of this bare road there were rows and rows of bright-yellow, bell-shaped tents. Hundreds and hundreds of tents, each one about twenty feet in diameter, occupying a forty foot by forty foot square.

There was also a parade ground, a square of bare earth two hundred feet long on each side. A unit of one thousand New Nithlings was drawn up there, in the process of being inspected by a very tall, very imposing New Nithling – or perhaps even a Denizen, because he was human-shaped and was wearing a pale-yellow uniform greatcoat of many toggles and considerable gold braid, topped by a Napoleon-style hat worn sideways over what from a distance Arthur thought was either his own metal-masked head or some kind of horrible metal replacement. This very tall commander was trailed by a dozen officers, or superior Nithlings, and in the mere second that it took Arthur to look down at the parade ground, he realised that this must be the mysterious leader of the New Nithlings.

He had no further time for thought. Sergeant Quicksilver was yelling and the Piper’s children were arraying themselves in a line across the top of the ramp, preparing their Nothing-powder pistols and carbines and power-spears and, in Quicksilver’s own hands, a muscle-fibre longbow.

‘Very good, ah, Sergeant,’ said Arthur. He had to struggle to keep his voice even. The whine of the spinning spike was very disturbing, rather like a human child complaining at an impossible pitch. The New Nithlings on the parade ground had also just noticed the intruders. The tall commander turned to look at them – and though he did not appear to say anything, there was a sudden flurry of activity among the officers behind him and shouted commands.

‘Take ’em five minutes to get here,’ said Quicksilver with a practiced glance. ‘All those tents in the way –’

She stopped talking as big kettle drums began to pound, in that same rhythm Arthur had heard in the attack on Fort Transformation. With the drums, New Nithlings emerged from almost every tent, like ten thousand hidden bees suddenly emerging from an innocent-looking square of honeycomb.

Arthur looked at Sir Thursday. He was next to the spike, his sword raised above his head. Suddenly he shouted a battle cry, a sound that rose above the noise of the spike and sent a jangling vibration down Arthur’s spine. Sir Thursday cut down at the whirling Nothing, slicing off a huge piece that hurtled clockwise through the air and came down on a bell tent, destroying it instantly, so all that remained were some sagging guy ropes hanging down a hole in the ground.

But the spike did not stop spinning, nor was there any notable hole in it, as if the Nothing it was composed of had simply filled the gap.

Sir Thursday scowled and cut at the spike again, with similar results.

‘Here they come,’ said Quicksilver. ‘Do you want to give the order to fire, sir?’

It took Arthur a second to comprehend that she was talking to him. He was staring down at the mass of New Nithlings that were being shouted and cajoled into ranks as they raced towards the bottom of the ramp to make up an assault force. There were lots of less-organised Nithlings on the sides of the ramp as well, some of them trying to climb the sides, with some success, though it was thirty feet to the top.

All the New Nithlings were uniformed, armed with the crackly lightning spears Arthur had seen before, and clearly well led. Though it was true they had greater physical variety among them than the Denizens, with extra limbs and distorted features, they bore no resemblance to the half-mad rabble Nithlings were supposed to be.

‘Yes, I’ll give the order,’ said Arthur as calmly as he could. ‘Musketoons first, then the power-spears. Quicksilver, you cover the left side and shoot the climbers. Suzy, you take the right and do the same with your pistols. Fred, you load for Suzy.’

Arthur drew his sword and moved to the centre of the line, with only half a glance back at Sir Thursday. Even that was enough to know that the Trustee was not making any real progress against the spike, though at least he was timing his cuts so that the pieces of Nothing flew off into the camp rather than cutting a swath through the Piper’s children on the ramp.

‘Wait for the order!’ called Arthur as musketoons were leveled and power-spears raised.

A formation of New Nithlings twelve across and ten ranks deep was almost at the foot of the ramp. Arthur looked at them stomping forward and knew there was no way they could stop them, or hold them off, or even survive. They’d have time for perhaps two volleys from the five musketoons, a cast of three power-spears, and that would be it. They would be overrun.

Overrun, thought Arthur. Just another way of saying that we’ll all be killed. Unless Sir Thursday can do something with the Key. Or we could try to get back on the Stair … only there’s no time. We’d never make it. They’d charge and cut us down … the last few for sure … which means me. Maybe that’s what Sir Thursday planned from the start.

The enemy drumming suddenly changed tempo, getting faster. The New Nithlings shouted and began their charge up the ramp. Suzy’s pistols went off, and Quicksilver’s bow twanged and twanged again as Arthur counted to three and shouted, ‘Fire!’ The musketoons banged and Nothing-powder smoke billowed up and Arthur shouted, ‘Throw!’ and the power-spears flew and Arthur shouted, ‘Holdfast!’ and moved into the front rank to be with the others, to hold the initial shock even if only for a few seconds and then –

A strange and unearthly sound filled the air. A breathy, high-pitched single note that sounded a little like a flute and a little like a whale singing and something entirely new and different as well.

The note stopped everything. In the case of the Piper’s children, they literally stopped, frozen in mid-action. All of them save Arthur, who looked at Fineold with his savage-sword half out of its scabbard and Jazebeth’s hand stopped with her fingers pulling back the lock of her musketoon.

Suzy was a statue on the brink of the ramp, a small snap-hance pistol in each hand, pointed down the right-hand side of the ramp. Quicksilver was just as still across from her, her bow dropped in favour of a triangular-bladed poniard.

The New Nithlings were not frozen, but they had stopped their charge and their climbing. Those on either side of the twelve-Nithling-wide ramp assault force were turning around and withdrawing, and the rest were moving apart to create an avenue of clear space up the middle.

The tall commander was striding up that avenue, holding a simple wooden pipe to lips that were invisible behind a metal mask of dull steel, playing that one impossibly pure, impossibly sustained note.

Arthur heard movement behind him and twisted around. Sir Thursday was there, his face red and screwed up in rage.

‘Traitors!’ he screamed. ‘Five minutes is all I asked!’

Before Arthur could do anything, Sir Thursday’s sword sliced through the air and connected with the frozen Private Fineold at Arthur’s side, cutting off his head with a single stroke. Then Sir Thursday rolled his wrists and, without stopping, swung the blade back again, straight at Corporal Jazebeth.

Without thinking, Arthur parried the blow. He got his savage-sword in the way, but it was as if the gravity-condensed steel were a mere twig. Sir Thursday’s sword snapped it in half, the impact making the broken sword fly from Arthur’s hand. Sir Thursday’s blow was hardly slowed, continuing to thunk horribly into Jazebeth’s neck.

Arthur half-fell and half-jumped back as Sir Thursday swung at him, changing the blow in midair from a cut to a thrust, flicking the point at Arthur. But the Denizen didn’t follow through. Instead he leaped to the right and began to draw steps with the blade, beginning to enter the Improbable Stair.

Arthur’s stomach muscles burned as he flipped himself fully upright. He took one swift glance around. The Nithling commander was twenty feet away, slowly walking up the ramp between the Nithlings, still playing that unearthly pipe.

Sir Thursday had one foot on his glowing step, his back to Arthur.

Arthur grimaced and reached alongside his cuirass under the armhole, feeling for the emergency dagger. But his fingers closed on a small plastic box. He had it out and in his hand before he remembered what it was.

I’m going to die, he thought. But I can save my family.

He threw the box at the spike and threw himself on Sir Thursday’s back just as the Trustee disappeared into the Improbable Stair.

Twenty-five

ARTHUR GOT HIS legs wrapped around Sir Thursday’s waist and his arms around his neck as he took his first step on the treacherous marble of the Improbable Stair itself. ‘Don’t try anything!’ warned Arthur. ‘If you do anything but move on the stair, I’ll throw both of us off!’

Sir Thursday growled something, a sound so inarticulate and full of anger it might have been a beast’s noise. But he kept plodding up the stair, carrying Arthur’s weight as if the boy were no more than a light rucksack.

After twenty steps, the Trustee spoke again.

‘You’ll die for this. Mutiny is mutiny, no matter who commits it. You have sealed your own end, Lieutenant.’

Arthur did not reply. He kept all his attention on Sir Thursday’s movements, not his speech. The Trustee had his sword in his hand, and he could easily angle it back and slide it into Arthur without warning. Arthur knew he had to be ready to throw all his weight to one side, even if it ended up being a dead weight. At least Thursday would be thrown off the Stair, hopefully to somewhere horrible where it would not be easy to get back on again.

Justice will be served, said a voice in Arthur’s head. The quiet, telepathic voice of the imprisoned Part Four of the Will. I nearly had him back there. You must make him angry again.

Make him angry? Arthur thought back. Are you as crazy as he is? I don’t want to make him angry. I don’t know how I’m going to survive as it is.

It is the only form of distraction that will work on Sir Thursday, replied the Will. Distract him, and I will free myself and deliver the Fourth Key to you, Lord Arthur. Then he may be brought to justice.

I’m not making him angry here, Arthur thought back at the Will.

He considered where the least worst place would be to make Sir Thursday angry for a moment. Then he spoke aloud.

‘There must be a big briefing room at the Citadel. For the Marshals and so on, to keep up with what’s going on. Particularly with the siege happening.’

‘There is my operations room,’ snarled Sir Thursday. ‘There is no siege. It is only an inconvenience.’

‘I want to come out in the operations room, then,’ said Arthur. ‘Take me there. Or I’ll throw us both off.’

‘My revenge … will be all the … sweeter for your insults,’ said Sir Thursday. Arthur could hear him grinding his teeth between words. ‘It is merely delayed.’

Arthur opened his mouth to answer, but he never had the chance, as unexpectedly, to him at least, they left the Stair and suddenly reentered the House. Immediately Sir Thursday struck back with his free hand, his bony fist smashing Arthur off his back and onto the floor. Dazed, the boy struggled to his feet. Before he could do any more than stand up, Sir Thursday was bellowing orders and there were plenty of Denizens rushing about to follow them.

‘Hold that traitor! All is revealed! The enemy is led by the Piper, and all Piper’s children must be executed before they can conduct any traitorous activity. Marshal Dawn, see to it immediately!’

Arthur felt his arms pulled back behind him. He struggled to lift his chin, finally managing it with the unintended help of someone who jerked his head back so they could get an arm around his neck.

He was in a large, domed room full of officers. The three standing with Sir Thursday were the tallest and most splendid, so they had to be Marshals Dawn, Noon, and Dusk. All three sported black eyes, and Noon had a bandage around his right hand as well, which suggested that they had been in recent fighting or that they did not always see things Sir Thursday’s way. Arthur thought the latter was more likely.

‘We’re not traitors!’ Arthur croaked as he was hauled backwards towards a door. ‘Sir Thursday killed two of his own soldiers! He’s not fit to command! I am an officer in the Glorious Army of the Architect too, and I demand to be –’

He got no further, as Sir Thursday crossed the room in a single leap and punched him in the stomach. It hurt worse than anything Arthur had ever felt, worse even than his broken leg. He couldn’t breathe and for several seconds thought he never would breathe, ever again. It was more frightening even than an asthma attack, because his chest felt actually broken, not just tight.

But after ten or twelve awful seconds, he did get a breath, as Sir Thursday’s attention was diverted by Marshal Dawn. Clad in the green of the Borderers, she stood out in a room dominated by scarlet headquarters uniforms, and also because unlike everyone else she strode towards Sir Thursday, rather than edging away from him.

‘The lieutenant is correct. He has leveled a serious charge and it must be heard.’

Sir Thursday’s eyes narrowed to slits and he glided like a snake across the floor towards the Marshal.

‘Must be heard? I have issued orders, have I not, Marshal Dawn? I want those Piper’s children killed.’

‘Regulations state –’

Sir Thursday slapped her in the face. She rocked back but did not try to defend herself, merely spitting out a tooth. Then she started again.

‘Regulations state that a court of enquiry –’

The next slap knocked her down and back onto her knees. But she stood up, and this time the other two Marshals marched forward to stand with her.

‘Sir, this is neither the time nor the correct –’ began Marshal Noon.