As Jenna and Septimus stood on the lonely slipway, the dark waters of the Moat to their right and the spreading Darkenesse of the Castle all around them, they heard an echoing, flip-flapping noise coming toward them.

"Quick, Jen. Let's get back inside."

Jenna nodded. The noise sounded horribly like an approaching Thing. Septimus was fumbling with the key when a voice called out, "Apprentice! Apprentice!"

The flustered figure of Marcellus Pye, with one shoe looking like a dog had mangled it, appeared from a gap between two houses and hurried toward them. "Thank goodness you are here." He bowed slightly to Jenna, as he always did, and then succeeded in annoying her - as he always did. "Princess. I did not recognize you at first. You do realize you are wearing the cloak of a true witch?"

"Yes. I do, thank you," said Jenna. "And before you ask, the answer is no, I will not take it off."

Marcellus surprised her. "I should hope not. It may prove useful. And you will not be the first Witch Princess in the Castle."

"Oh." Jenna was not entirely pleased. She had rather assumed that she was the first Witch Princess.

"Marcellus," said Septimus urgently. "Jenna needs to stay somewhere safe. I thought your SafeChamber - "

Marcellus did not let Septimus finish. "It is not safe here, Apprentice. Miss Djinn knows I have a SafeChamber - all Chambers are declared to the Chief Hermetic Scribe - and I fear our Chief Hermetic Scribe has already given away our secrets." Marcellus shook his head sadly. He hated to see what had happened to the Manuscriptorium. "There are Things abroad already," he continued. "They will come here soon enough, and Princess Jenna will be trapped like a rat. We must go somewhere the Darke Domaine will have trouble finding."

"But the Darke Domaine is spreading fast," said Septimus. "It will soon be everywhere. Jenna should leave the Castle."

"Sep, I'm actually still here," said Jenna, annoyed. "And I am not leaving the Castle."

"Quite right, Princess," said Marcellus. "Now, I believe that the Domaine will have some trouble getting into the Ramblings, and even once it's inside it will not find it easy to spread. So I suggest we head there and . . . what is that Young Army term, Apprentice?"

"Regroup?" Septimus offered.

"Ah, yes. Regroup. Ideally, what we need is an overlooked little fleapit down a dead end, with an outside window."

Jenna knew exactly where to find one. She pulled out the key that Silas had given her not so very long ago.

"What's that?" asked Septimus.

"It's a key, Sep," teased Jenna.

"I know it's a key. But where to?"

Jenna grinned. "An overlooked little fleapit down a dead end, with an outside window," she said.

Marcellus Pye closed the door of his house behind him with a sigh and looked up at his dark windows. Septimus had insisted he blow out all his candles and it had made him feel quite depressed.

"Come now, we must go," said Marcellus.

"I'll Call Spit Fyre," said Septimus. "Something must have spooked him. He can't have gone far."

Marcellus looked doubtful. He'd got along just fine without dragon flight for more than five hundred years and he wasn't in a hurry to change things. But Septimus was already letting out the ululating Call, which reverberated off the densely packed houses on Snake Slipway and made the Alchemist shiver. It was a primeval sound, Marcellus thought, one that went back way beyond Alchemie.

They waited nervously on the slipway, glancing at the shadows, imagining movements.

After a few minutes Marcellus whispered, "I do not believe your dragon is coming, Septimus."

"But he has to come when I Call," said Septimus, worried.

"Maybe he can't, Sep," whispered Jenna.

"Don't, Jen."

"I didn't meant that he was . . . well, I . . ." Jenna stopped. She could see she was only making things worse.

"Dragon or no dragon, we can wait no longer," said Marcellus. "With care we can travel short distances through the Darke Domaine. My cloak has certain . . . abilities, shall we say, and you, Apprentice, have a small tinderbox that may prove useful." Jenna shot Septimus a questioning look. "And you, Princess, will be protected well enough with your membership of . . ." Marcellus peered at the markings on her witch cloak. "My, you don't do things by halves, do you? The Port Witch Coven! Now, we must go. We will travel by the Castle Canyons."

"Castle Canyons?" asked Jenna, who liked to think she knew most things about the Castle. "I've never heard of them."

"I suspect not many Princesses ever do. Although now you have other, er, allegiances, you might find that will change," Marcellus said with a smile. "The Canyons are not, shall we say, salubrious places. Those using them generally have reasons to hide. However, I know them well and we can slip through the night unnoticed. I am much practiced at the art."

That did not surprise Jenna. Marcellus threw his long black cape around himself with a dramatic swirl and, equally theatrically, Jenna followed suit with her witch's cloak, pulling the hood over her head to cover her gold circlet. Compared with his companions, Septimus felt a little conspicuous in his Apprentice green. He followed in their footsteps, feeling like an apprentice thief shadowing his masters.

Almost immediately Marcellus ped into a tiny gap between the houses. An ancient sign half hidden behind some ivy announced its name: SQUEEZE GUTS OPE. With the rough bricks snagging at their cloaks, they threaded their way through the warren between the jumble of houses that were packed in behind Snake Slipway. Their footsteps made no noise as they trod on years of leaves, moss and the occasional soft mound of a small dead animal. Feeling like a small animal himself scuttling through its burrows, Septimus kept glancing up, hoping to see the sky. But the dark of the moon and the snow-laden clouds gave nothing away. Once or twice he thought he saw a star, only to be obscured by the black shape of a chimney or a twist of a roofline as he turned yet another corner. The only light came from the comforting glow of his Dragon Ring as he held his right hand out in front of him.

As they went deeper in, the Canyons narrowed, sometimes so much that they were forced to walk sideways, squeezing past towering walls that threatened to press them flat. Septimus had an image of them squashed between the walls like the dried herbs Sarah Heap kept between the pages of her herb book. He longed to be able to stretch his arms out wide in all directions without his knuckles hitting brick, to be able to run freely in any direction he wanted to, not crawl like a crab between rocks. With every step he felt as though he were going deeper into a place from which he would never escape.

Septimus tried to take his mind off the encroaching walls by looking out for lighted candles in windows but there were hardly any windows to see. The sheer sides of stone rising up on either side blocked any view, and few people had put a window in a wall that looked out onto another wall no more than an arm's length away. But once or twice Septimus saw the telltale glow of a candle way up above them, shining onto the opposite wall, and his spirits raised a little.

At last they followed Marcellus into a wider gap and the Alchemist raised his hand in warning. They stopped. At the end of the gap was a bank of Darke Fog - they had reached the edge of the Darke Domaine.

Jenna and Septimus exchanged anxious glances.

"Apprentice," said Marcellus, "it is time to open your tinderbox."

Jenna watched with great interest as Septimus took a battered tinderbox from his pocket and pried off the lid. She saw him draw something from it, but what it was, she could not tell. He muttered some strange words that she could not catch and threw his hands upward. She got the impression that something floated down very slowly and settled onto him, but she couldn't be sure. He looked no different. In fact, it seemed more like a mime than anything else - the kind of thing they had had to do in drama classes in the Ramblings Little Theatre, which Jenna had always found rather embarrassing.

However, Marcellus and Septimus seemed satisfied, so Jenna guessed something must have happened. And then she did notice a change - the light from Septimus's Dragon Ring seemed more fleeting somehow, as if thin gauze was moving across it. And, when she looked at Septimus and tried to catch his eye, she realized that something about him eluded her. He was there, and yet he was not there. A little spooked, Jenna stepped back. Sometimes she felt Septimus was part of things that she would never fully understand.

Marcellus regarded his two charges closely. They were as prepared as they could ever be, he thought. Now they would have to put things to the test - it was time to step into the Darke Domaine. He beckoned them to the end of the passageway. They stopped where the Fog rolled in front of them, close enough to reach out and touch, and Marcellus said, "I will go first, then you two walk together. Keep a steady pace, breathe quietly. Keep your mind clear, for it will tempt you to stray from our path with beguiling thoughts of those you once loved. Do not react to anything and above all, do not panic. Panic draws Darke things to it like a magnet. Understood?"

Jenna and Septimus nodded. Neither could quite believe they were about to step into the shifting wall of Darkenesse of their own free will. Both Septimus's Darke Disguise and Jenna's witch cloak protected them from the beguiling thoughts that drew people into the Darke Domaine. It was odd, thought Jenna, that her witch cloak allowed her to see the Darke Domaine for what it truly was: a terrifying blanket of evil.

Once again they exchanged glances, then together they followed Marcellus into the Darke Fog.

Septimus's Darke Disguise felt like a second skin. He moved easily through the thick Darke Fog, but both Marcellus and Jenna struggled. Jenna's witch's cloak gave her less protection - it did not totally enclose her in the way Septimus's Darke Disguise did and it was not nearly as powerful. Marcellus's cloak gave even less protection - he did not dabble with the Darke quite as much as he liked people to think he did. But any remnants of Darke offer protection in a Darke Domaine and Marcellus and Jenna managed to struggle along, even though they felt as though they were wading through glue and breathing through cotton wool. Waves of fatigue washed over them, but by force of will they managed to keep going.

After some minutes they came to a halt - they had reached Wizard Way. Marcellus peered cautiously out. He looked right and left and right again in exactly the way Jenna remembered Sarah doing when they used to cross the Way when she was little. Then Jenna had known what Sarah was looking out for, but now she had no idea what it was Marcellus was watching for - or how he could possibly see anything. Marcellus beckoned them forward and they stepped out into Wizard Way.

It was not a good place to be. The Darke Domaine felt heavier here and it moved around them like a living thing. Sometimes they felt something brush past them, and once a Thing's finger poked at Marcellus but he swept it off with a Darke curse and the Thing scuttled away. They walked steadily down the middle of the Way and concentrated on breathing slowly and calmly, in and out, in and out, as they measured their steps along the familiar - yet now so strange and frightening - Wizard Way.

As they walked on, Septimus began to get a strong sensation that there was something approaching behind them. It was a sense that he had learned to develop over his Apprentice years and he knew it was good. Remembering what Marcellus had said, he fought the urge to look back, but he could not rid himself of the feeling of a great creature bearing down on them fast. So fast that if they didn't jump out of the way right now . . . Septimus gave Marcellus and Jenna a hefty shove - not so easy in a Darke Domaine - and leaped to the side.

He was just in time. A huge black horse thundered past, his eyes wide and wild, mane streaming in the Darke and Lucy Gringe clinging on, screaming silent, terrified screams.

Thunder's flight had the effect of clearing a temporary path through the Darke. Marcellus quickly recovered himself and steered Jenna and Septimus into the horse's wake, where they moved quickly along the horse-shaped tunnel that Thunder had created through the swirling blackness. For Marcellus and Jenna it was a relief to be out of the weight of the Darke, although they knew it would not last long - the space was already being invaded by a dull murkiness. At the end of the tunnel they could see that Thunder had halted, and the muffled sounds of shouting drifted toward them.

Jenna risked an excited whisper to Septimus. "Mum . . . I can hear Mum."

Septimus was not sure it was Sarah. It sounded more like Lucy Gringe to him, and there was a deeper voice there too.

Thunder's tunnel was slowly collapsing under encroaching wisps of Darke Fog moving into the space like smoke from a fire burning something foul. The sounds at the end of the tunnel faded into ghostly whispers, but in those faraway echoes, Jenna was absolutely convinced she could hear Sarah's voice. Suddenly, much to Marcellus's disapproval, she broke into a run. She could not bear the sound of her mother being obscured by the Darke once more. She had to get to her this time.

Jenna flew along the space, forcing Septimus and Marcellus to follow the departing witch's cloak, which spread out behind her like a huge black wing. They arrived at a scene of which Septimus, let alone Marcellus, could make no sense at all.

At first all Septimus could see was Thunder, stamping and tossing his head, rolling his eyes from side to side - a terrified horse longing to flee. A man had hold of his mane and was talking to him in a low voice without much effect, it seemed to Septimus. On the other side of the horse, mostly obscured by Thunder's bulky body and starry horse blanket, he saw the hem of Lucy Gringe's embroidered robes and chunky boots and then he saw Jenna's witch's cloak - with four feet coming from beneath it. And then, as Thunder did a sudden turn, he saw Jenna. She was wrapped in Sarah's arms and had enfolded her mother in her cloak as if to never let her go. Lucy was also hanging onto someone . . .

"Simon!" gasped Septimus. He turned to Marcellus. "My brother. It had to be. Of course it did. He's behind all this. So that's what his creepy letter was about: Beware the Darke. I get it now."

Simon heard every word. "No!" he protested. "No, it's not that. It is not. I - "

"Shut up, you toad," snapped Septimus.

Marcellus did not know what was going on. But what he did know was that the middle of a Darke Domaine was not the place to have a family argument.

"Believe me, this is nothing to do with me," said Simon, half pleading, half angry at being blamed yet again for something he had not done.

"Liar!" exploded Septimus. "How dare you come here and - "

"Be silent, Apprentice!" snapped Marcellus.

Shocked at being spoken to in that way, for Marcellus was always scrupulously polite, Septimus stopped in mid sentence.

Marcellus took advantage of the surprised silence. "If you value your lives, you will - all of you - do as I say," he said with great command. "Immediately."

The peril of their situation hit home. Everyone - even Simon - nodded.

"Very well," said Marcellus. "Jenna, you know where to go so you will lead the way with the horse. It will help that you will both clear the air a little." Simon went to protest but Marcellus stopped him. "If you wish to survive you will do as I say. Septimus, your mother is very weak; you will find your Disguise will stretch to two. It will shield her from the worst of it. I will follow with the young lady and with Simon Heap - for I presume you are he?" Simon nodded. "We shall move in this formation: one, two, three. It is the most efficient way to move through viscosity. We will go silently as one. There must be no dissent. None whatsoever. Is that understood?"

Everyone nodded.

And so like winter geese they set off in their V formation, Jenna with Thunder, Septimus and Sarah Heap sharing the Darke Disguise, followed by Marcellus, who had thrown his cloak around Simon on one side and Lucy on the other.

As they set off, Jenna muttered their destination under her breath. She didn't know why she did, but as soon as she had, Jenna felt sure that she would find the way. She moved quickly out of Wizard Way and into the alleyways that would take her to the nearest entrance to the Ramblings. Deep in the Darke Fog Jenna found that the silence suited her. It allowed her to concentrate, and there was something about the witch's cloak that gave her a feeling of safety within the danger that surrounded them. She moved easily through the Darke, and when she glanced around to check that everyone was still following her, she saw that, like Thunder, she was clearing a path for those behind. Not for the first time she wondered at her cloak's powers.

There was no one in the Castle that terrible night who moved through the Darke Fog with anything approaching Jenna's lightheartedness. Her happiness at finding Sarah safe overwhelmed everything. She hardly cared about the Darke Domaine or Simon's sudden, suspicious appearance. She had her mum back and that was all that mattered.

And every route she had learned for her Extramural Ramblings Certificate all those years ago led to the very place she was now headed: The Big Red Door, There and Back Again Row.