He leapt in like a child given an unexpected treat. Gotrek followed him in showing no emotion whatsoever, his enormous axe slung lightly over his shoulder. Felix stepped tentatively inside and felt the metal floor flex under his feet. It was not a reassuring feeling.

The engineer slammed the cage door shut and suddenly Felix felt like a prisoner in a cell. Then another engineer pulled a lever and the engine's pistons started to rise and fall.

Felix's stomach gave a lurch as the cage began to move and the ground fell away beneath them. Instinctively he reached out to grab one of the bars and steady himself. He gulped in air as nervous as he had been before the battle with the skaven. He noticed that he could see the ground through the small holes in the floor beneath his feet.

"Wheel" went Snorri happily. The faces of the dwarfs on the ground shrank beneath him. Soon the machines were small as child's toys and the vast bulk of the airship swelled ever larger above them. Looking down gave Felix a very unsettling feeling. It wasn't as if they were really going that much higher than the topmost battement of the castle, it just felt so much further.

Perhaps it was something to do with the motion, or the wind whistling past through the bars of the cage but Felix felt very much afraid. There seemed to be something unnatural about just standing there with all your muscles rigid and your knuckles white from gripping cold metal while the girders of the metal tower glided past. His heart almost stopped as the cage came to rest and all motion ceased save for the slight swaying of the cage on its hawsers.

"You can let go now, manling," Gotrek said sarcastically. "We've reached the top."

Felix pried his grip loose to allow the engineer at the top to open the cage. He stepped through the opening and out onto a balcony. It was a structure of metal struts that ran around the top of the metal tower. The chill wind whipped his cloak and brought tears to his eyes. He felt suddenly frozen with fear when he saw how high he was above the ground. He could now no longer see all of the airship. It was too large for all of it to fit within his field of vision. A metal gangplank ran between the top of the tower and a door in the lower part of the airship's side. On the far side of it he could see Varek and Borek and the others waiting for him.

For a moment he could not make himself move. The ground was at least three hundred paces below him and that metal gangplank could not be that firmly attached to the airship or the tower. What if it gave way below him and he fell? There would be no chance of surviving a drop of this magnitude. The pounding of his heart sounded loud in his ears.

"What is Felix waiting for?" he heard Snorri ask.

"Move, manling," he heard Gotrek say and then a powerful shove sent him stumbling forwards. "Just don't look down."

Felix felt the fragile metal bridge strain under his weight and for a moment thought that it was going to give way. He virtually bounded forward on to the deck of the airship.

"Welcome aboard the Spirit of Grungni," he heard Borek say.

Varek grabbed him and pulled him further past. "Makaisson wanted to call this ship the Unstoppable," the dwarf whispered, "but for some reason my uncle wouldn't let him."

Felix slumped beside Makaisson at the helm of the airship. He had been forced to duck as he came below. The airship had been designed with dwarfs in mind and so the ceilings were lower and the doors wider than they would have been for humans.

The engineer was dressed differently today. He wore a short leather jerkin with a massive sheepskin collar raised against the cold. A leather cap with long earflaps covered his head. There was another flap cut in the top for Makaisson's crest of hair. Goggles covered the dwarfs eyes, presumably as some protection against the wind if the front window was to shatter. Heavy leather gauntlets enclosed the dwarfs large hands. Makaisson turned and looked up at Felix, beaming with all the pride a father might show when pointing out the achievements of a favourite child.

As far as Felix could tell, some of the controls resembled those of an ocean-going ship. There was an enormous steering wheel which looked rather like a cartwheel, except that it had handgrips around the rim at strategic intervals to allow the pilot a comfortable grip. Felix imagined that by swinging the wheel the pilot could alter the direction of the craft. Beside the wheel were set a group of levers and a square metal box bearing all manner of strange and alarming gauges. Unlike with a ship, the pilot stood at the bow of the craft behind a shield of glass so that he could see where he was going. Looking out the window over the prow Felix could see there was a figurehead, some bearded and roaring dwarf god, which Felix presumed was the dwarf god, Grungni.

"Ah can tell yer impressed," Makaisson said, glancing over at Felix. "An so ye should be—this is the biggest and best airship ever built. Actually, as far as ah ken it's only the second one ever built."

"You're certain that this thing will fly?" Felix asked nervously.

"As certain as ah am that ah had ham fur breakfast. The balloon, that big thing above yer heed, is full of liftgas cells. There's enough o' the stuff up there to keep twice oor weight airborne."

"Liftgas?"

"Och, ye ken, it's stuff that's lighter than air. It naturally wants to rise skyward, and as it does it taks us way it."

"How did you manage to collect the stuff if it's lighter than air. Wouldn't it just float away?"

"A sensible enough question, laddie, an' one that shows ye hay the makin' o' an engineer. Aye, it's naturally rarer than hen's teeth but we make the stuff oorselves doon there in the toon. At least oor alchemist dae. Then we pipe it intae the balloon above us."

"The balloon." The thought worried Felix even more. It made him think of the tiny hot air balloons he had made of paper as a child. It seemed inconceivable that such a thing could lift a weight of solid metal, and he said so.

"Aye well, is a lot stronger than hot air and the balloon above yer heed is no made o' metal, nae metter what it looks like. It's made of mare resilient stuff. Alchemists made that as weel."

"What if the gas leaks out?"

"Och, it woudnae dae a thing like that! Ye see inside that big balloon are hunnerds o' wee balloons. We call them gasbags or cells. If yin bursts it disnae metter much, we'll still hae plenty o' lift. Ivver half they wee balloons would hae tae burst before we lost altitude and even then it would be gradual. It just woudnae be natural for them tae aw burst at yince."

Felix could see the sense of this arrangement. If the balloon above held thousands of smaller balloons, it was indeed unlikely that they could all be burst at once—even if they were attacked with hundreds of arrows, only the gasbags on the outside would be punctured, if arrows could even penetrate the outer structure of the balloon. Clearly Makaisson had given considerable thought to the safety of his creation.

Somewhere at the rear of the ship a bell rang out. Felix looked around to see that the gangplank had been slid into place and a railing had been swung back round to cover the gap. He felt marginally safer.

"That's the sign that we're supposed to be awa'," Makaisson said. He pulled one of the smaller levers close to hand and a steam-whistle sounded. Suddenly engineers swarmed across the ship to take up positions all around. From the ground below Felix heard cheering.

"Brace yersel!" shouted Makaisson and tugged another lever. From somewhere below the ship came the sound of engines starting up. Their roar was almost deafening. At the sides of the ship the dwarfs were starting to reel in the hawsers on great drums, for all the world like a horde of sailors weighing anchor. Slowly Felix began to sense movement. Currents of air stroked his face. The airship began to rise and to move forward. Almost unwilling, he moved to the side of the ship and looked out through the porthole. The ground was starting to slip away below them, and the Lonely Tower complex fell away behind. The tiny figures of the dwarfs on the ground waved up at them and on impulse Felix waved back. Then he was overwhelmed by a sickening sense of vertigo and had to step back from the window.