Fear lent her strength, and Leaf managed to crawl up to the headboard railings. She leaned over Arthur and screamed, ‘What do we do now?’

She didn’t sound like she was enjoying this adventure.

‘Hold on!’ Arthur shouted, looking past her at the towering, office-block-high wall of water that was falling towards them. If it broke over the bed, they would be smashed down and pushed deep into the sea, never to surface.

The crest of the wave curled high above them, blotting out the dim, grey light of the sky. Arthur and Leaf stared up, not breathing, eyes fixed on the curving water.

The wave didn’t break. The bed rode up the face of the wave like a fisherman’s float. As it neared the top, it tipped up almost vertically and started to roll over, until Arthur and Leaf threw their weight against the curl.

They were just in time. The bed didn’t roll. It levelled out as they made it to the crest of the second wave. They balanced there for a few seconds, then the bed started its downward slide once more. Down into another sickeningly deep trough in front of another giant, blue-black, white-topped cliff of moving water.

But the third wave was different.

There was a ship surfing down it. A hundred-and-sixty-foot-long, three-masted sailing ship with sails that glowed a spectral green.

‘A ship!’ yelled Leaf, hope in her voice. That hope rapidly fled as the bed continued to run down into the trough at alarming speed, and the ship surfed down the opposite side even faster still.

‘It’s going to hit us! We have to jump!’

‘No!’ shouted Arthur. If they left their makeshift raft he felt sure they’d drown. ‘Wait!’

A few seconds later, waiting seemed like a very bad decision. The ship didn’t waver in its course, a great wooden missile coming at them so fast that it would run right over them and the crew probably wouldn’t even notice.

Arthur shut his eyes when it got within the last twenty yards. The last thing he saw was the ship’s bow plunging down into the sea, then rising up again in a great spray of froth and spray, the bowsprit like a spear rising from the water.

Arthur opened his eyes when he didn’t feel the shocking impact of a ship ramming them. The ship had turned just enough at the last instant to meet the bed in the very bottom of the trough between the waves. Both had lost speed, so that the bed would be right next to the ship for a matter of seconds. It was an act of tremendous seamanship by the captain and crew, particularly in the middle of such a mighty swell.

Through the blowing spray, Arthur saw two looped ropes like lassoes come down. One loop fell over Leaf. The other, clearly aimed for Arthur, fell over the left bedpost instead. He scrambled for it and started to lift it off. But before he got it clear, both ropes went taut. Leaf went up like a rocket, up towards the ship.

The other rope tipped the bed over.

Arthur lost his grip and tumbled into the sea. He went down several feet, his breath knocked out of him. Through the veil of water and spray, he saw Leaf and the bed spinning up to the ship’s rail high above. The bed went up several yards, then the rope came free and it fell back down.

He kicked as best he could with one immobilised leg, and struck out with his arms, desperate to get back to the surface and the ship. But by the time his head broke free of the sea and he got a half-breath of spray-soaked air, the vessel was already at least fifty yards away, surfing diagonally up the wave ahead, moving faster than the swell. New sails unfurled and billowed out as he watched, accelerating its passage.

The bed was much closer, perhaps only ten yards away. It was his only chance now. Arthur started to swim furiously towards it. He could feel his lungs tightening, an asthma attack closing in on him. He would only be able to swim for a few minutes at most. Panicked, he threw all his energy into getting back to the bed, as it started its rise up the front of the following wave.

He just made it, grabbing a trailing blanket that had twisted through the bars at the end of the bed. Arthur frantically pulled himself along that, hoping it wouldn’t come loose.

After a struggle that used up all his remaining strength, he managed to haul himself up onto the mattress and once again wedge his arms through the bars.

He shivered there, feeling his breath getting more restricted as his asthma got worse. That meant that wherever he was, it wasn’t the House. This sea was somewhere in the Secondary Realms.

Wherever it is, I’m probably going to die here, Arthur thought, his mind numbed by cold, shock, and lack of breath.

But he wasn’t going to go easily. He freed his right hand and pressed it against his chest. Perhaps there was some shred of remnant power from the First Key in his hand, or even of the Second Key.

‘Breathe,’ whispered Arthur. ‘Free up. Let me breathe.’

At the same time, he tried to stop the panic that was coursing through his body. Over and over, inside his head, he told himself to be calm. Slow down. Take it easy.

Whether it was some remaining power in his hand or his efforts to stay calm, Arthur found that while he still couldn’t breathe properly, it didn’t get any worse. He started to take stock of his situation.

I’m kind of okay on the bed, he thought. It floats. Even wet blankets will help me stay warm.

He looked up at the wave the bed was riding up. Maybe he’d got a bit used to these enormous waves or just couldn’t get any more terrified, but it did seem a bit smaller and less curling at the top than the first few. It still scared him, but it felt like less of a threat.

He thought about what else he might have. He was wearing hospital pyjamas and a dressing gown, which weren’t much good for anything. The cast on his leg looked like it might be disintegrating already, and he could feel a dull throbbing ache deep in the bone. His Immaterial Boots kept his feet warm but he couldn’t think of anything else they could be used for. Other than that, he had — The Atlas! And the Mariner’s whalebone disc!

Arthur’s hand flashed to his pyjamas pocket and then to the multiple strands of floss he’d woven into a string for the whalebone disc. The Atlas was still in his pocket. The Captain’s medallion, as he’d come to think of it, was still around his neck.

But what use were they?

Arthur wedged his good leg through the bars and curled up as much as he could into a ball. Then he gingerly let go with his hands and got out the Atlas, keeping it close to his chest to make sure that it couldn’t get washed away. But as he’d half-expected, it wouldn’t open. He slowly put it back in his pocket.

The Captain’s whalebone disc, on the other hand, might work. Tom Shelvocke was the Mariner after all, son of the Old One and the Architect (by adoption), a man who had sailed thousands of seas on many different worlds. He’d told Suzy Turquoise Blue to warn Arthur to keep it by him. Perhaps it might summon help or even communicate with the Captain.

Arthur pulled the disc out from under his pyjama top and looked at the constellation of stars on one side, and then at the Viking ship on the other. They both looked like simple carvings, but Arthur thought there had to be some kind of magic contained in them. Because it seemed more likely to be of immediate help, Arthur concentrated on the ship side, and tried to will a message to the Captain.

Please help me, I’m adrift on a bed in the middle of a storm at sea, he thought over and over again, even whispering the words aloud as if the charm could hear him.

‘Please help me, I’m adrift on a hospital bed in the middle of a storm at sea. Please help me, I’m adrift on a hospital bed in the middle of a storm at sea. Please help me, I’m adrift on a hospital bed in the middle of a storm at sea . . .’

It became a chant. Just saying the words made Arthur feel a little better.

He kept up the chant for several minutes, but had to give up as his lungs closed down and he could only just get enough breath to stay semiconscious. He lay next to the headboard, curled up as much as he could with one leg straight and the other thrust through the bars. He was completely sodden, and the sea continually sloshed over him, so he had to keep his head up to get a breath.

But the waves were definitely getting smaller and the wind less ferocious. Arthur didn’t get a bucketful of spray in his eyes and mouth whenever he turned to face the wind.

If I can keep breathing, there’s some hope, Arthur thought.

That thought had hardly crossed his mind when he felt an electric thrill pass through his whole body, and his stomach flip-flopped as if he’d dropped a thousand feet in an aircraft. All the water around him suddenly looked crisper, clearer, and a more vivid blue. The sky turned a charming shade of eggshell blue, and looked closer than it had before.

Best of all, Arthur’s lungs were suddenly clear. He could breathe without difficulty.

He was in the House. Arthur could feel it through his whole body. Even the ache in his broken leg subsided to little more than an occasional twinge.

Hang on, he thought. That was too easy. Wasn’t it?

This thought was interrupted by what sounded like an explosion, far too close for comfort. For a moment Arthur thought he was being shot at by a full broadside of cannons from a ship like the one that had taken Leaf. Then it came again, and Arthur recognised it as thunder.

As the bed reached the top of another wave, he saw the lightning — lightning that stretched in a line all the way across the horizon. Vicious forks of white-hot plasma that ran in near-continuous streams between sea and sky, constant thunder echoing every flash and bolt.

The bed was being taken straight towards the lightning storm. Every wave that it rode up carried it forward. There was no way to turn it, stop it, or avoid the collision.

To make matters as bad as they could possibly be, the bed was made of metal. It had to be the biggest lightning conductor for miles. And any lightning that hit would go through Arthur on its way to connect with the steel frame.

For a few seconds, Arthur’s mind was paralysed by fear. There seemed to be nothing he could do. Absolutely nothing, except get fried by a thousand bolts of lightning all coming down at once.

He fought back the fear. He tried to think. There had to be something. Perhaps he could swim away. . . but there was no way he was strong enough to swim against the direction of the swell. It would be better to die instantly by lightning than to drown.

Arthur looked at the line of lightning again. Even in only a few minutes he’d got much closer, so close he had to shield his eyes from the blinding bolts.

But wait, thought Arthur. The ship that took Leaf went in this direction. It must have gone through the lightning storm. I just have to get through. Maybe Lady Wednesday’s invitation will protect me …

Arthur checked his pocket. But there was only the Atlas.

Where could the invitation be?

The pillows were long gone, lost overboard, but the sheets were partially tucked in. Arthur dived under the drenched linen, his hands desperately groping into every corner as he tried to find the square of cardboard that might just save him.

The bed rose up the face of a wave, but did not reach the crest. Instead, bed, wave, and boy rushed towards the blinding, deafening barrier of thunder and lightning that was the Line of Storms. The defensive inner boundary of the Border Sea, which no mortal could cross without permission.

The penalty for trying was a sudden, incendiary death.

Three

ARTHUR NEVER SAW the lightning or heard the water boiling where the bolts struck, the noise lost in the constant boom of thunder. He was under the sheet, a soggy piece of cardboard clutched in one trembling hand. He didn’t even know if it was the invitation from Drowned Wednesday, his medical chart from the end of the bed, or a brochure about the hospital telephones.

But since he was still alive a minute after the blinding glow beyond the sheets faded, he guessed it must be the invitation in his hand.

Arthur slowly pulled his head out from under the sheet. As he blinked up at the clear blue sky, he instinctively took another deep breath. A long, clear, unrestricted breath.

As the bed moved in the mysterious current, the swell it was riding subsided to a mere ten or twelve feet, with a much longer interval between waves. The wind dropped, and there was no blowing spray. It also felt much warmer, though Arthur couldn’t see a sun. He couldn’t see any clouds or lightning either, which was a plus. Just a brilliant blue sky that was so even and perfect that he supposed it must be a painted ceiling, like in the other parts of the House.

Arthur took several more deep breaths, revelling in the rush of oxygen through his body. Then he took stock of his situation once more. The one thing he had learned about the House was that you couldn’t take anything for granted. This warm, rolling sea might turn into something else at any moment.

Arthur tucked the Captain’s disc back under his pyjama top and slid Lady Wednesday’s sodden and barely legible invitation next to the Atlas in his pocket. Then he braced his cast against the headboard, stood up, and looked around.

There was nothing to see, except the sea. The bed rode too low in the water. Even standing up, Arthur’s view was blocked by the next wave. What he could see was much closer and immediately obvious.

The bed was sinking. Even in this calmer ocean, the mattress was now totally submerged, losing its buoyancy as it absorbed more and more water, the steel frame dragging it down.

It wasn’t going to sink in the next five minutes, but it was going to sink.

Arthur sighed and sat back down, water splashing almost up to his waist. He looked at the cast on his leg and wondered if he should take it off. It was very lightweight and it hadn’t dragged him down before, but that had been a truly panic-driven swim and it would be hard to swim any real distance with it on. But if he took it off, his leg might snap apart again or hurt so much that he couldn’t swim anyway.

He decided to leave the cast on and got out the Captain’s disc again. This time he just held it in his hand and tried to visualise the ship with the glowing green sails coming back to pick him up.