The Darke Disguise did not spare Septimus the hole in the riverbed - through which he was sucked like a noodle into a greedy mouth - or the swash of the cave below. But it protected him like a glove and gave him the Darke Art of Suspension Underwater - something that Simon had spent many uncomfortable months with his head in a bucket learning to perfect. As Septimus swirled slowly around the underwater cave his thoughts unwound; he opened his eyes and realized that he was still alive.

The Darke Art of Suspension Underwater imparted an oddly distancing effect. The reason for this was to allay panic and so to conserve oxygen, although Septimus - indeed, most practitioners of the Art - did not realize this. It also allowed the eyes to see perfectly through the normal watery blurriness and this made moving underwater feel closer to flying than swimming. And so, as Septimus swam along with the circular currents of the egg-shaped cave, he found to his surprise that he was actually enjoying the sensation of being underwater. His Dragon Ring glowed brightly, turning the water around him a beautiful milky green and, when he drifted near the walls of the cave, the light made the crystals in the rock glitter as he passed.

But the Darke Art of Suspension Underwater does not last forever. After some long, hazy minutes, Septimus began to feel breathless and twitchy. Pushing aside the early signs of panic, he swam upward toward what he hoped was the surface and some air to breathe, only to hit his head with a painful crack on the roof of the cave. The panic welled up. There was no surface - there was no air.

Septimus sank a little and, holding his Dragon Ring out in front of him, he swam fast, looking upward, hoping to see some kind of space where he could draw a breath. Just one deep, beautiful breath of air was all he needed . . . just one. He was so busy looking up that he almost did not notice a flight of steps cut into the rock in front of him. It was only when the light from his Dragon Ring showed a strip of lapis lazuli set into the edge of a step, and above it another, and then another, that he realized he had found his way out. Eagerly his hands followed the steps up to an underwater gap in the rocky roof, through which they disappeared. Desperate now to take a breath, Septimus pulled himself up through the rock and emerged gasping into the freezing air of the Darke Halls.

The cold shocked him. His teeth chattering, water cascading off him, Septimus got shakily to his feet. In his preparation for his Darke Week, he had read ancient descriptions of what many now thought was no more than a mythical place beneath the earth, but he knew now they were true. All described what he was experiencing: a musty smell of earth and the stifling feeling of being pressed down by the surrounding rock and, accompanying everything, an eerie wail that seemed to drill into his bones. They had also described an overwhelming fear, but Septimus, insulated by the Darke Disguise covering him from head to toe, felt no fear - just elation at being alive and able to breathe once more.

Septimus drew in a few more luxurious deep breaths and took stock. Behind him was the egg-shaped hole in the ground through which he had just emerged; the faint light from his Dragon Ring caught the glint of gold from the lapis lazuli strip on the top step. In front of him was the unknown: a deep, thick darkness. Septimus had no landmarks, nothing to navigate by, just the sensation of a colossal empty space. All he had to go on was Simon's advice. And so he took it. He turned left and began to walk.

As he got into his stride, Septimus's mind began to emerge from the state of panic into which it had descended during his last few seconds under water and he began to think clearly once more. According to Marcellus, all he had to do was walk through the Darke Halls until he reached the lower entrance to the antechamber to Dungeon Number One. It was there, Marcellus had said, that he was most likely to find Alther. He has not long been Banished, Apprentice. He is unlikely to have yet roamed far. Marcellus had even described the entrance to him - in such detail that Septimus suspected that the Alchemist had actually seen it for himself. A portico, he had called it: a square-cut doorway flanked on either side by ancient lapis pillars. Marcellus had calculated it to be about a seven-mile walk, which was the distance as the crow flies from the Bottomless Whirlpool to the Castle.

Septimus set a brisk pace. Seven miles at that speed should take him about two hours, he calculated. It was a monotonous journey. He saw very little except the pressed earth floor beneath his feet, and when he held his Dragon Ring out in front of him he saw nothing but the circle of light. It was a little disorientating, but he walked with a feeling of excitement - Alther was near. Soon he would see him and say, "Oh there you are, Alther," as though he'd bumped into the ghost while strolling down Wizard Way. He tried to imagine what Alther would say and how pleased the ghost would be to see him. To prepare for that moment, Septimus went over in his mind the Banish Reverse that Marcia had taught him. It was complicated and, like the Banish itself, it must last for precisely one minute and be completed without hesitation, repetition or deviation.

Septimus walked on, his boots thudding dully against the earthen floor. He had the sensation of moving through a massive space, but not an empty one. All around him was a dismal wailing as if the wind was crying out in despair and loss. As he pushed through the dank, earthy atmosphere, small gusts of air brushed past him, some warm, some cold and some with a feeling of intense evil that took his breath away and reminded him that he was in a dangerous place.

After some time - surely much longer than an hour and a half - Septimus began to suspect that the Darke Halls were a whole lot bigger than he or Marcellus had thought. One of the ancient writers had called them "The Infinite Palaces of Wailing." Septimus had noted the Wailing but had paid little attention to the Infinite Palaces bit. But the cavern he had been walking through was surely as big as a dozen Castle Palaces - and it showed no sign of ending. The enormity of his task suddenly hit him. There were no maps to the Darke Halls; everything they knew was based on legends or on the writings of a handful of Wizards who had ventured there and returned to tell the tale. Most of these had drifted quickly into madness - not the most reliable of sources, thought Septimus, as his weary feet plowed onward.

And so it was with huge relief that Septimus at last saw a landmark appearing out of the gloom - a great square-cut gap in the rock, flanked on either side by two lapis lazuli pillars. It was exactly as Marcellus had described the entrance to Dungeon Number One. With his spirits soaring Septimus hurried toward it. Now all he had to do was to walk through and find Alther on the other side.

As he got closer to the portico Septimus noticed something white at its foot, and as he drew nearer still, he saw what it was. Bones. Clean and completely white - except for a thin brass ring with a red stone on the left little finger - the skeleton was sitting propped against the wall, the skull tipped at a jaunty angle toward the pillars as if pointing the way through.

Feeling it was wrong to pass casually by, Septimus stopped beside the bones. They had belonged to someone small, probably no taller than he had been a year ago. They looked fragile, sad and lonely, and Septimus felt a wave of sympathy for them. Whoever they had been had somehow survived the Bottomless Whirlpool only to find a haunted, freezing desert awaited them.

A sudden wail of wind blew through the portico and chilled him, even through the Darke Disguise. A bout of shivering overtook Septimus and he decided it was time to go through to the antechamber to Dungeon Number One; time to find Alther and do what he had come to do. He nodded respectfully to the bones and stepped through the portico.

The antechamber to Dungeon Number One was not what Septimus had expected - it seemed much the same as the empty space he had been walking through before. And there was no sign of Alther - there was, in fact, no sign of any ghosts at all. According to the texts, the antechamber was the most haunted place on earth, mostly by the ghosts of those thrown into the dungeon over the centuries. One of the great fears that Dungeon Number One held was the knowledge that those who died there were never seen as ghosts. All fell victim to the thrall of the Darke Halls and spent their entire ghosthood below the ground, with no possibility of ever seeing the people or places they had once loved ever again. Many quite reasonably preferred to stay with the company of other ghosts rather than roam the "Infinite Palaces of Wailing."

The antechamber to Dungeon Number One was described as a circular walled chamber lined with black bricks, the same as those used to build the little round brick pot that marked the top entrance to the dungeon. And if those descriptions were right - and Septimus believed they were - then he was most definitely not in the antechamber to Dungeon Number One.