T hey followed the long, scuffling tracks away from the hut. The tracks led over a small stone bridge that Snorri had marked on the map, then up a steep slope and down into another valley beyond. As they walked through the tall trees at the head of the broad valley, all around was silence and snow; not a breath of wind stirred the branches. Once or twice they caught a glimpse of the Thing far below, speeding down the slope with its odd, lurching gait, but the white of its robes made it hard to spot against the snow and it drew ever farther ahead until they lost sight of it.

Still following the tracks, the compass needle led them down to a frozen marsh on the valley floor. It was noticeably colder here. The mix of ice and marsh mud crackled beneath their feet and the tall, black spikes of reed that stuck up through the snow snagged on their wolverine-skin cloaks. As they continued on a downward slope, the marsh gave way to a wide frozen stream, along which the Thing had traveled in long, sliding strides. Jenna picked up Ullr and placed him on top of her backpack. The cat perched precariously and surveyed the scene in a disapproving manner. Slipping and sliding, they set off along the ice, leaning forward to balance their backpacks. Soon they got into a steady skating rhythm and picked up speed along the smooth ice of the stream.

The stream widened and led them into the lower reaches of the valley. Septimus, who was in the lead, suddenly saw a huge bank of thick white fog rising in front of them. He skidded to a halt and Beetle cannoned into him, closely followed by Jenna and Ullr, who toppled onto the ice with a loud meow.

"Ouch," said Beetle, dusting himself off and struggling to his feet. "You might have warned us you were putting on the brakes."

"Didn't have time," said Septimus. "Look." He pointed to the fog.

Beetle whistled between his teeth. "Where did that come from?"

"I saw it," said Jenna, "but I thought it was snow."

It was true - the fog was exactly the same color as snow. It stretched from left to right as far as the eye could see and blended seamlessly into the gray-white snow-filled sky. Jenna did not like fog; it reminded her of the time when she had sat marooned inside a Magykal fog near the Marram Marshes, listening to the click of a pistol no more than a few feet away, aimed at her heart. "Do you think the Thing is in there, waiting for us?" she whispered.

"No," said Beetle. "Look - the Thing saw it before we did. There are the tracks." The lopsided tracks had left the frozen stream, doubled back on themselves and disappeared up the hill and into the trees.

As they scanned the tracks, a long low rumble began to shake the ground. Deep within the fog, something was coming.

"Can you hear that?" asked Jenna, wide-eyed and pale.

Septimus and Beetle nodded.

"Run?" said Beetle as the ground vibrated through the soles of his boots. "Now?"

"Where to?" asked Jenna, glancing around. Nowhere looked safe to her.

Septimus shook his head. "No...no. It's going away now. Listen. It's passed by. Whatever it was."

"Whatever it was," muttered Beetle, "I would not have liked to have been in the way."

Not so very far away, at the top of the hill, the Thing stopped and looked down on the three figures standing uncertainly on the edge of the fog bank. It grimaced, contorting Ephaniah's rat mouth into a vicious snarl. Just a few more careless steps, it thought, and the job would have been done. But no matter - let them take their chance with the Foryx on the precipice path. And if they miss the Foryx then it will do exactly as its new Master had instructed. The Thing respected its new Master. Slowly and clumsily, it turned away and, increasingly tired of the unwieldy body it had saddled itself with, lumbered off through the snow.

Back at the frozen stream Septimus was looking at the compass, shaking it in irritation. "Bother, bother, bother. Stop it." The needle, however, took no notice of being spoken to and carried on spinning wildly. "Jen," he said, "we'd better look at the map. I think we've reached the edge of the hole."

"Literally," Beetle said with a gulp. "Look." The fog was a mixture of eddies and swirls that drifted up in the air. It was constantly shifting, in some places dense, in others almost clear - and it was in one of these clear patches that Beetle had seen that no more than a few steps away the frozen stream had become a waterfall of ice, plunging over the edge of an abyss.

"Oh..." Septimus swayed and closed his eyes. A horrible feeling of vertigo shot up from the soles of his feet and made his head spin.

Beetle and Jenna crept forward and warily peered over. The fog rose, swirling in long tendrils that wrapped themselves around their feet and chilled them to the bone. Beetle crept even closer to the edge; he picked up a rock from the pile of stones beside the waterfall and hurled it into the chasm.

They counted the seconds, waiting for the sound of the rock hitting the bottom, but after one whole minute they had still heard nothing. A sudden gust of wind caught Beetle's cloak and sent it noisily flapping.

"Beetle!" Jenna gasped, grabbing hold of his sleeve. "You're too close. Come back." This was exactly the kind of thing that Beetle's mother would have done. If it had been his mother, Beetle would have become extremely petulant and deliberately stood even closer to the edge - but not with Jenna. A decidedly unpetulant Beetle allowed himself to be pulled away.

Septimus, meanwhile, had no intention of going anywhere near the edge. He had found a nice, solid tree a safe distance away and was leaning against it, his head still spinning. He hadn't felt vertigo like this in a long time - certainly not since he had had the Flyte Charm. How he wished he had the Flyte Charm now. Trust Marcia, he thought, to take away the one thing that would have made this whole expedition actually easy. He took a deep breath. Not more than a few feet away was the deepest chasm he had ever come across. Septimus didn't need to look over the edge to know that - he could feel it all the way up from his feet, and he knew.

He remembered the Young Army saying: On the brink, stop and think. Now that he was a little older, the rhymes he had learned parrot-fashion seemed to make sense in a way they hadn't at the time. And so, leaning against the tree - as close to the brink as he was willing to get - Septimus began to think. He thought about the Queste. He thought he really should tell Jenna and Beetle about the Questing Stone. He should tell them to go on without him and leave him to do the Queste - wherever that would take him. But then he thought of walking away from Jenna and Beetle, of leaving them alone to find Nicko, and he knew he couldn't - he just couldn't.

Jenna's voice broke into his thoughts. "Look, Sep," she said, laying the map on the snow beneath the tree. Then, "No, Ullr, go sit somewhere else," she said, gently pushing the cat off the paper. Ullr looked unimpressed. He sat down in the snow and began to lick his paws. Jenna kneeled down and ran her finger around the edge of the hole where the missing piece should have been. "It's funny," she said, "that the edge of the hole in the map is at the edge of a chasm. It's almost as if it were a real hole, if you see what I mean. I figure the House of Foryx is over there." She pointed into the fog. "It all makes sense now. That must be what Aunt Ells called the great pit."

Suddenly Beetle said, "Look! There's the bridge." He whistled. "That is some bridge."

Far away to the left they could just make out the spindly outline of a structure leaping high into the air and disappearing into the fog. It looked beautiful - a delicate tracery of fine lines like a spider web suspended in space. And then the fog closed over it once more and it was gone.

"That's it!" said Jenna, excited. "All we have to do is cross that bridge and we're there. Isn't that great?

"Great," said Septimus with a sinking feeling that started in his stomach and went all the way down to his feet. "Really great."

They set off toward the bridge, following the edge of the chasm but keeping - on Septimus's insistence - a safe distance away. After a while it became apparent that they were, for the very first time in this strange place, actually following a path. The snow looked trampled by animals rather than humans and Septimus could not help but wonder what kind of animals. Whatever they were, they had the kind of droppings that Septimus preferred not to step in.

As the morning wore on, the sun rose above the fog and the heavy snow clouds in the sky began to clear. But the fog remained, moving and shifting like a great brooding creature beside them.

Sometimes Septimus thought he heard distant voices far below, somewhere deep within the fog.

Once, Jenna stopped, convinced she had heard someone cry out.

The thought that soon they would have to step onto a bridge and walk into this shifting, brooding bank of fog preoccupied all three - and Septimus in particular. He dropped back and let Jenna and Beetle move ahead. As he trudged behind the two wolverine-cloaked figures with their Forest backpacks - and a small orange cat with its fur puffed out - something else began to preoccupy Septimus. Very reluctantly, but unable to resist, he put his hand into his tunic pocket and drew out the Questing Stone. Hardly daring to look, he closed his eyes and then - remembering how near they were to the edge of the precipice - he opened them again fast. The Stone was yellow. Yellow to guide you through the snow, thought Septimus with a sinking feeling.

Jenna turned around suddenly. "Hey, Sep. You okay?"

Septimus quickly shoved his hand back in his pocket. "Yeah," he said, heavily. "Fine."

All along their journey beside the chasm, the path had steadily been curving to the right as it led them around in a great circle, but the fog had always obscured the bridge. But now, as they approached a thick-set, snow-covered tree standing close to the path, two tall, iron pillars appeared out of the fog.

Tall, thin and strangely beautiful, the pair of pillars leaned slightly backward, glistening with damp from the mist, their tops tapering and disappearing into the swirls of fog that drifted up from the chasm below. With a feeling of dread, Septimus knew they had arrived.

"Wow..." breathed Beetle. "Look at that."

Septimus thought he would rather not.

The bridge itself was a precarious structure of wooden planks laid across two thick cables that rose in a curve and disappeared into the fog. How long did it go on for? he wondered. Was it just a few more yards or was it for miles? Septimus had a horrible feeling that the latter was more likely. There was something about the curve that made it look like a wide span. It was an odd structure; from the top of the pillars, four cables swooped down. Two stretched far behind them and were buried in the snow and the other two followed the curve of the bridge and vanished into the fog. Septimus searched for something that might reasonably be called "sides" or possibly "handrails," but all he could see was what seemed to him to be a couple of pieces of string. He'd had nightmares about bridges like this - but none of them had been this bad.

Septimus glanced at Jenna and Beetle, strangely relieved to see that they did not look exactly overjoyed at the prospect of the bridge either. He was about to suggest they have some of Sam's fish - anything to delay the awful moment when he would have to step onto what looked like no more than a piece of beginner's knitting - when he heard a movement in the tree behind them.

"That'll cost you," said a harsh voice from above.

They leaped into the air at the sound of the first new voice they had heard since Sam had said good-bye.

"I said, it'll cost you," the voice repeated.

Septimus looked up. "Where are you?" he asked.

"Up the tree. And I'm coming down."