Arthur closed his eyes as they hit . . . and fell over something, going no faster than if he’d tripped walking around his bedroom with his nose glued to a book.

Arthur opened his eyes, flailed his arms, and smacked into the ground. He lay there for a second, feeling a tremendous surge of relief as he felt honest-to-goodness solid matter under his hands. He still held the Key, no longer glowing, and the absence of significant pain suggested no bones were broken or other damage done.

But where was he? He became aware that he was lying on grass – he could see and feel that. Slowly Arthur got to his feet and looked around. The first thing he noticed was that the light was strange. Dim and cool and orange-pink, like sunset when the sun hung low and orange. But there was no sun in sight.

Arthur stood on a bare, high hill of close-mown grass that looked down upon a sea of white . . . no, not a sea. A fog bank had settled to the limits of the horizon. And there were buildings in the fog, dim shapes that he couldn’t quite make out. Spires pierced the grey-white mist, and towers, but none was close enough for him to see any identifying features.

Arthur looked up next, expecting to see the sky. But he didn’t and he instinctively crouched at what he saw instead.

There was no sky. There was a ceiling in its place, a vast domed ceiling of dull silver that stretched for miles in every direction. Its epicentre was about six hundred feet directly above the hill where he stood. Swirls of purple and orange moved across the silver surface of the dome, providing what little light there was.

‘Pretty, ain’t it?’ said a voice behind Arthur. A man’s voice, deep and slow. Not threatening, just the sort of remark anyone at a lookout might make to another visitor.

Arthur jumped and nearly fell over again as he twisted around to see who spoke. But all he could see was an enormous free-standing door of dark-oiled wood between tall gateposts of white stone, standing on the crest of the hill. Door was an inadequate word, Arthur thought. It was more of gate, as it was easily three or four times the size of his parents’ garage door.

The door was decorated with wrought-iron climbing vines and clever curlicues that formed different patterns and designs depending on where you looked and the angle of view. Rather like a puzzle. In a few seconds Arthur made out a tree, which could also be a sea horse if he tilted his head, and that horse’s tail could also be a comet surrounded by stars, with the stars joining together to make a ship . . .

Arthur blinked and saw completely different shapes and pictures. He blinked again and tore his gaze away. The door was dangerous. He felt that the patterns and shapes could trap him into staring at them forever.

And where was the person . . . or whatever it was . . . who had spoken to him? He looked around, but there was only the strange door and the bare hill. A vast door that appeared to go nowhere, standing stark and alone.

Arthur walked around it and was unsurprised to see that the other side was exactly the same. Perhaps the door was some sort of sculpture, he thought, only meant to make an artistic statement. But deep down, Arthur knew that if the door was to open, he would not see the hill on the other side.

‘Shift change in a moment,’ said the voice. ‘Then you’ll see something worth seeing.’

‘Where are you?’ asked Arthur.

‘Where?’ asked the voice. It sounded surprised. ‘Ah. Not exactly . . . wait a moment . . . a step to the left . . .’

The ironwork on the door shimmered, and the patterns formed into the shape of a man. Then the shape stepped out of the door. The iron tracery became flesh and blood, and standing in front of Arthur was a tall, calm-looking man who looked about the same age as his father, Bob, though he had long white hair that flowed down and over his shoulders. Like Mister Monday, Sneezer, and Noon, he was wearing very old-fashioned clothes. In his case, a blue swallow-tailed coat with gold buttons and a single gold epaulette on his left shoulder, over a snowy white shirt, tan breeches, and shiny knee boots with turned-down tops. He held a scabbarded sword in his left hand, gripping it casually below the hilt. Two golden tassels fell over his wrist. It didn’t look like he was about to draw the weapon.

‘Pardon me,’ the figure said. ‘Sometimes I forget myself. I’m the Lieutenant Keeper of the Front Door. Allow me to salute the bearer of the Lesser Key of the Lower House.’

He stood at attention and saluted, then offered his hand.

‘Arthur Penhaligon,’ said Arthur. He automatically shook hands. The Lieutenant Keeper’s flesh felt strangely smooth and cool, though it was not repellent. Arthur was careful to switch the Key to his left hand and keep a tight grip on it, as he wondered why this strange character had called it the Lesser Key.

‘Where am I?’

‘Why, the Lower Atrium of the House,’ said the Lieutenant Keeper. ‘On Doorstop Hill.’

‘Right,’ replied Arthur. He was about to ask another question but didn’t, as his next thought was upstaged by a shaft of brilliant light that suddenly shot up from the foot of the hill, extending all the way to the ceiling of the dome. It was joined a moment later by a beam coming down, and then there was a multitude of beams going up and down, as if hundreds or even thousands of intense up-and-down lights were being switched on. All together they created an illumination that was similar to, but not quite the same as, daylight.

Now Arthur could see through the fog, which slowly began to break up and drift apart. There was a whole city below the hill, a city whose architecture was strikingly reminiscent of how the House looked in his own world, though here the buildings were separate, sitting on broad streets rather then being jumbled all together.

‘What . . . what are those beams of light?’

‘Elevators. It’s shift change,’ explained the Lieutenant Keeper. ‘The end of night, and the coming of the light. Work must be done, and the elevators bring workers from above and below, taking the nightwatchers to their rest and conveying all the matters and moments that must be dealt with in this new day.’

‘What work? What . . . who?’

‘I haven’t time to answer questions,’ said the Lieutenant Keeper. ‘Though it is shift change, my relief has not marched up for ten thousand years, nor has the Captain Keeper made his rounds. I must return to my post. It is at shift change that danger often comes, and I should be on guard. Though I will offer this counsel: Hide the Key from prying eyes. And I will give you my spare shirt and watch cap, so you do not look too much the stranger. Good luck, Arthur Penhaligon.’

He saluted again, stepped back into the door, and became ironwork once more. A second later, even that man-shape flowed into many different puzzle pictures and Arthur had to force himself to look away before his mind was trapped into following the ever-changing images. He missed the ironwork twisting into a shirt and a knitted cap, which then fell out at the boy’s feet.

Arthur put the shirt on over his own clothes. It was white linen, had long tails, and was much too big. It also had a weird detachable collar and no buttons on the cuffs, but Arthur had to fold the sleeves back several times anyway. The watch cap was a dark blue circular cap made from some sort of felt material.

Hide the Key from prying eyes. Arthur thought about that. It sounded like good advice, and there was something about the Lieutenant Keeper of the Front Door that he instinctively liked and trusted. But how could he hide the Key if he needed to hold on to it to breathe normally?

Or did he? Perhaps things were different here. Wherever here was, it was certainly not his own world. Arthur hesitated, then experimentally opened his hand and balanced the Key on his palm. He felt no different, though of course the metal was still in contact with his skin.

Arthur went down on one knee, hesitated again, then gently tipped the Key onto the grass. He half-expected his lungs to seize up as the Key fell, but they didn’t. His breath still came easily, and he wasn’t struck by any sudden pains or tightness of the chest. He felt just the same. Which, he suddenly realised, was very well. Energetic and full of unusual vigour.

So he didn’t need to touch the Key all the time here – wherever here was. Arthur picked it up and, after a moment’s thought, pushed it through his belt. With the Lieutenant Keeper’s shirt coming down almost to his knees, the shining metal of the minute hand was completely hidden.

That done, he looked down at the town or city that was spread out below. He could see people all over the streets now and could hear the hustle and bustle, though there were no cars or any of the noises of a modern city. The only vehicles he could see – and there were few of them – appeared to be drawn by horses. Or something like horses. Arthur couldn’t be sure from this distance, but he didn’t think they looked quite right.

‘I suppose the first step is to go down and try to find someone who can tell me something about . . . about everything,’ he said to himself. It looked safe enough. The weird beams of light continued to shoot up and down all over the place, but he’d noticed they only emanated from the tops of buildings, so even if they were actually huge laser beams or death rays he would be able to avoid them. And from up here, the city and the people looked ordinary, if extremely old-fashioned, without cars or traffic lights or power lines.

He would just have to keep a very wary eye out for Fetchers and Noon and Mister Monday and anyone who showed too much interest in him or looked dangerous. It was a pity he’d lost his backpack, he thought, and the salt in it. But perhaps that wouldn’t work here anyway.

Arthur looked around the hill once more, but it was only a delaying tactic. He had to go down to the city because there was no choice. He couldn’t go back. Even if he knew how, that wouldn’t solve anything. The only way to find a cure for the Sleepy Plague was to forge ahead.

Arthur thought of Leaf and Ed again for a moment. They were the best prospects for friends he’d met in the new school. If they survived the plague. Anything could be happening back home. Arthur thought of the incredibly swift spread of the virus that had killed his birth parents. It had exploded through the population, spreading from a single known carrier to infect more than five thousand people in the first twenty-four hours. By the second day, almost fifty thousand people were sick. When Emily’s team found a vaccine only eighteen days after the initial report, and with extreme quarantine in place, almost a million people were dead.

I wish I hadn’t remembered that statistic, thought Arthur. But there was no point standing around simply hoping. He had to do something.

‘Rock and roll,’ muttered Arthur, thinking of his father. He punched his fist in the air and set off down the hill towards the closest row of buildings and the cobbled lane that ran behind them at the foot of the hill.

Half an hour later, Arthur was deep in the heart of the city, and extremely confused. There were people everywhere – at least they looked like people. But they were all dressed in the fashions of more than a hundred and fifty years ago. Every man wore a hat of some kind, every woman too, though they mostly went for bonnets and caps. Even the children – not that there were many of them – wore flat caps or obvious hand-me-downs that were too big for them. There was also incredible variation in the quality of the clothes. Some of the people were dressed in little more than the ragged remnants of what appeared to be several very different and incompatible wardrobes. Others were immaculate, with spotless coats, stiff white shirt-points, flowing cravats, shining waistcoats, and gleaming boots. None of the children fell into this latter category. All the kids were dirty and dressed in incredible hodgepodges of secondhand clothing.

Even weirder than the people’s clothes was what they were all doing. Arthur had expected that he would find all the usual city activities going on, with shops and restaurants and bars and businesses and people shopping and buying and selling, or just walking around and chatting to one another.

There was none of that. There was tremendous hustle and bustle with people going in and out of the buildings and talking in the streets and carrying boxes and pushing little carts around, swapping loads and exchanging boxes and bags and chests and barrels. There were carts drawn by horse-like animals, but they weren’t horses. They looked like horses from a distance, but they had three distinct toes instead of hooves, no manes, glittering ruby eyes, and their skin had the sheen of metal rather than horse-flesh. Definitely not horses.

But the horses weren’t the weirdest thing about the city. Even stranger was the fact that everything being moved around or exchanged (or whatever the people were doing) was either paper, something like paper, or related to writing in some way.

There were men carrying piles of papers, their chins pressed down on the top sheets to make sure they didn’t blow away. There were men whose coat pockets were stuffed with rolls of parchment, with wax seals hanging off the rolls. There were people pushing carts loaded with stone tablets that had lines of writing carved into them. There were women exchanging leather document cases. Girls running with string bags full of envelopes and loose papers. Boys struggling with small barrels marked SECOND-BEST AZURE-BLUE INK.

Arthur wandered through a marketplace full of street stalls, but every stall was the same, selling quills and cutting feathers for use as quills, with partially plucked geese running around everyone’s feet. A line of men in leather aprons passed carrying bundles that Arthur recognised as papyrus reeds, from his project on ancient Egypt last semester. Four women struggled by with a huge sheet of beaten gold that had strange symbols hammered into it.

With all the hustle and bustle and papers and stuff being transported everywhere, there was also an incredibly high level of disorganisation wherever Arthur wandered. It seemed like a lot of the people didn’t really know what they were doing and were doing something simply because they were afraid to not be doing something. Everyone was busy, always with paper, or stone tablets, or papyrus scrolls, or pens, or ink, or chisels. Arthur didn’t see a single person just standing around, or sitting, or chatting without an armful of papers.