As Beetle resumed his place at head of the Call Out, the person who should have been leading it was immured in the basement of a house on Snake Slipway. Not far above him, a loud knocking on the front door by a breathless Wizard went unheard.

Septimus was listening to Marcellus Pye discussing the dangers of, and defenses against, the Darke. Time was ticking on. Very slowly. So far there had been at least an hour's worth of dangers, if not more.

Alchemist and Apprentice were sitting inside a tunnel-like, windowless chamber. The atmosphere was oppressive; the air was fuggy with candle wax fumes, and a faint taint of lingering Darke made Septimus edgy. Unlike Marcellus Pye, who sat opposite him in a comfortable tall-backed chair, Septimus was perched uncomfortably on a bumpy stone bench. Between them was a small table, thick with candle grease, on which yet another burning candle added its contribution.

Marcellus, however, looked at ease. He was in his secret SafeChamber with his Apprentice, instructing him in the defense of the Darke, and that - as far as he was concerned - was how things should be. A SafeChamber was something every self-respecting alchemist always possessed, but never admitted to. In what Marcellus now called "his first life" as an alchemist, five hundred years in the past, he had installed his SafeChamber between two adjoining rooms in the basement of his house. It occupied the space so cleverly that none of the subsequent inhabitants had ever noticed the few feet lost from each room.

Marcellus had constructed the chamber himself - he had had no other choice. In the days of the Castle alchemists, one of the drawbacks of the profession had been that it was impossible to get a builder. Once a builder knew that a job was for an alchemist, he would suddenly become very busy, or fall off a ladder and "break a leg," or have to go away to a distant relative's sickbed. Whatever the excuse, he would certainly never be seen again. The reason for this was that the perils of working for an alchemist had become legend among Castle builders, passed down from Master to Apprentice: "Never work for an alchemist, lad," (or lass, but usually lad). "As soon as the job's done, you'll surely be found floating facedown in the Moat to keep the secrets of what you've just built. However much gold they offer you, it just isn't worth it. Believe me." Although this wasn't true for all alchemists, it has to be said that there was some basis for this belief.

Marcellus Pye possessed many talents but building was not one of them. The outside of the chamber was passable because Marcellus had covered his rough brickwork by putting up great sheets of wooden paneling in both the affected rooms. However, the inside of the chamber was a mess. Marcellus had not realized how hard it was to build walls that went up straight - and stayed that way - so the walls grew closer and closer together, almost meeting at the top. Once he had installed the false wall behind which he kept his most arcane treasures, the SafeChamber was no more than a claustrophobic corridor.

Septimus was almost lulled into a trance by the flickering of a multitude of candles perched in the various nooks and crannies provided by Marcellus Pye's unusual approach to bricklaying. The chamber was streaked black with the soot from their flames, and thick rivulets of wax ran down the walls, glistening in the yellow light. The only thing that kept Septimus from drifting off was the way the bricks in the wall pressed their sharp corners into him as though they were jabbing at him with angry fingers. Every now and then he would wriggle uncomfortably and lean against another, slightly different, pointy bit.

"Stop fidgeting and pay attention, Apprentice," said Marcellus Pye sternly from his comfortable chair. "Your life may - indeed, it most probably will - depend upon it."

Septimus suppressed a sigh.

At last Marcellus got down to the reason that Septimus had come to see him. "You will, I presume, be attempting to retrieve Alther Mella's ghost from the Darke Halls tonight?"

"Yes. Yes . . . I'm going to the Darke Halls. At midnight." As he said the words Septimus felt a thrill of excitement mixed with fear. Suddenly it all began to feel very real.

"And you will seek to enter the Darke Halls through the Dungeon Number One Portal?"

"Yes, I will. Isn't that the only place where you can get in?" Septimus asked.

Marcellus Pye looked quizzical. "Not at all," he said. "But it is the only place you can get to in time for midnight tonight. There are other Portals, some of them extremely effective for matters like this, where you might find your timing is less important. However, none are in the Castle."

Leaving Septimus to wonder why Marcia hadn't told him about these other, possibly more effective Portals, Marcellus took the candle from the table and got up from his chair with a small groan. Looking like the old man he really was, the alchemist shuffled along the length of the chamber to the false wall at the end, which was, Septimus noticed, paneled like the room outside. Marcellus pressed his hand onto one of the panels, slid it to one side and reached into the space behind. Septimus heard the clink of glass on glass, the rattle of small dried things in a metal box, the thud of a book, then a relieved, "Got it!"

As Marcellus shuffled back, Septimus very nearly leaped to his feet and ran for it. The light from his candle threw dramatic shadows onto the alchemist's face, and as he advanced toward Septimus, hand outstretched, Marcellus looked exactly as he had when Septimus had first seen him - a five-hundred-year-old man grabbing at him, pulling him through a glass into a secret world below the Castle. It was not a good moment. It unsettled Septimus more than anything else had in the tense buildup to his Darke Week.

Unaware of the effect he had had, Marcellus Pye resumed his place next to Septimus. He looked pleased. "Apprentice, I have in my hand something that will give you safe passage through the Portal and into the Darke."

He unclasped his fist to reveal a small, dented tinderbox. Septimus felt horribly disappointed. What was Marcellus thinking? He owned his own tinderbox and it was a lot better looking than that one. And it probably worked better too - Septimus prided himself on being able to get a fire going in fifteen seconds. He and Beetle had had a fire-start competition not long ago and he had won best of five.

Marcellus handed him the tinderbox. "Open it," he said.

Septimus did as he was asked. Inside were the usual components of a tinderbox - a small, pronged wheel, a flint, some thin strips of cloth infused with the Castle's well-known, highly flammable wax and some dried moss.

Septimus had had enough. Marcia's parting shot came back to him: "Alchemie stuff is nothing but smoke and mirrors, Septimus. All talk and no do. None of their stuff ever did work. It was complete rubbish."

Septimus got to his feet. Marcia was right - as usual. He had to get out of the oppressive little chamber dripping with candle wax, fusty with Darke secrets. He longed to be part of the everyday Castle world once more. He wanted to run through the streets, breathe the cold fresh air, see the myriad of Castle lights twinkling in the windows, watch people as they promenaded back and forth admiring - or not - their neighbors' lights. But more than anything, he wanted to be with people who weren't fussy five-hundred-year-old alchemists who thought you were still their Apprentice.

Marcellus had other ideas. "Sit down, Apprentice," he said sternly. "This is important."

Septimus remained standing. "No, it's not. It's an old tinderbox. That's all. You can't fool me."

Marcellus Pye smiled. "It seems I already have, Apprentice. For this is not what it appears to be."

Septimus sighed. Nothing ever was where Marcellus was concerned.

"Patience, Apprentice, patience. I know this chamber is cramped, I know it is stuffy and foul, but what I am going to show you can only be revealed here. It will not survive outside the Darke for long." Marcellus looked up at Septimus, his expression serious. "Septimus, I cannot - I will not - let you venture defenseless into the Darke. Sit down. Please."

With another sigh, Septimus reluctantly sat down.

"You see," said Marcellus, picking up the tinderbox, "like all Darke Disguises, this is not what it appears to be. As you too must be when you go into the Darke."

"I know. Masks, MindScreens, Bluffs - I've done all that stuff with Marcia."

"Well, of course you have." Marcellus sounded conciliatory. "That is no more than I would expect. But there are some things to which even the ExtraOrdinary Wizard does not have access. That's what we alchemists are - or were - for. We kept in touch with the Darke. We went where Wizards did not dare."

This was no more than Septimus had suspected, given Marcia's warnings about alchemists, but this was the first time he had heard Marcellus admit to it.

Marcellus continued. "As an Alchemie Apprentice it is only right that you too should know how to work with the Darke. It is all very well the Wizards sticking their heads in the sand like one of those birds . . . oh, what are they called?"

Septimus was not sure. "Chickens?" he suggested.

Marcellus chuckled. "Chickens will do nicely. Like chickens, they peck at what is in front of them but they do not understand what it truly is. Sometimes they call it something else, like Other, or Reverse, but that does not change anything. Darke remains Darke whatever you call it. So now, Apprentice, you must decide whether to take your first step into the Darke the Alchemie way - and see what is really inside the tinderbox - or the Wizard way, and see no more than an old flint and some dried-up moss. Which is it to be?"

Septimus thought of Marcia and he knew what she would say. He thought of Beetle and he really wasn't sure what he would say. And then he thought of Alther. Suddenly Septimus had the oddest feeling that Alther was sitting right next to him. He turned and thought he saw a momentary flash of purple, a suggestion of a white beard. Then it was gone, leaving Septimus with the certain knowledge that he would never see Alther again unless he said, "The Alchemie way."

Marcellus smiled with relief. He had been extremely worried at the thought of Septimus venturing into the Darke in the customary just think good thoughts and it will be all right Wizard style. The old Alchemist was also just a little triumphant. He had, for the moment, won his Apprentice back.

"Very wise," Marcellus said. "Now you stop being a chicken and embark on your first conscious step into the Darke. Septimus, you understand that this is only to be taken if you truly wish to do it. Do you?"

Septimus nodded.

"Then say it."

"Say what?"

"That you want to do this. Say 'I do.'"

Septimus hesitated. Marcellus waited.

There was a long pause. Septimus had the heady sensation of being about to step over a threshold that even Marcia had not crossed.

"I do," he said.

As though someone had thrown a switch, all the candles in the chamber went out. The temperature plummeted.

Septimus gasped.

"We must not be afraid of the Darke." Marcellus's voice came through the fumes of extinguished candles. Septimus heard the Alchemist click his fingers. At once the candles burst back into flame, but the chamber remained cold -  so cold that Septimus could see clouds of breath misting the air.

Marcellus now had Septimus's full attention. "Apprentice, your first step is to choose a name to use when you are dealing with the Darke. Wizards - if they venture this far - usually reverse their whole name, but they do not realize how dangerous this is. You will never be free of the Darke if you do this, you can always be Found. We Alchemists know better. We take the last three letters from our name and reverse them. I suggest you do that."

"S - U - M," Septimus said.

Marcellus smiled. "Sum: I am. Very good. If you have to use your name, this is what you say. It is close enough to pass for the truth, but not true enough for you to be Found. Now we get to the reason we are here: Apprentice, do you wish to take on the Darke Disguise?"

Septimus nodded.

"Say it," prompted Marcellus. "I cannot take you through these steps on a mere nod of the head. I must be clear that you wish to proceed."

"I do," said Septimus, his voice trembling a little.

"Very well. Apprentice, place the tinderbox over your heart, like so . . ."

Septimus held the tinderbox over his heart. It sent a stab of cold right through him like a dagger of ice.

Marcellus continued his instructions. "Keep your hand stone still - no more fidgeting. Good. Now repeat these words after me."

And so the old Alchemist began, using Reverse words that Septimus had never heard before, words that he suspected Marcia too had never heard. They chilled him more than the icy press of the tinderbox, more than the freezing air inside the chamber. By the time Septimus had spoken the last words - "I dnammoc siht ot eb: draug sum" - his teeth were chattering with cold.

"Open the box," said Marcellus.

At first Septimus thought the tinderbox was empty. All he could see was the dull gray metal of the insides, and yet when he looked closely he was not sure that it was metal that he was seeing. It looked misty, as though something was there and yet not there. Tentatively, as though something might bite, he put his finger into the box. His finger told him that there was indeed something in the tinderbox - something soft and delicate.

"You have found it." Marcellus looked pleased. "Or rather, it has found you. That is good. Now take it out and put it on."

Feeling as though he was playing a "let's pretend" game with Barney Pot, Septimus pinched his thumb and forefinger together and got hold of something elusive, barely there. It felt like pulling spiderwebs from a jar - spiderwebs that the spider in the jar did not want him to have. Septimus pulled hard, and as he raised his hand high he saw that he was drawing a long stream of gossamer-thin fabric from the tinderbox.

Marcellus Pye's dark eyes shone with excitement in the candlelight. "You've done it . . ." he whispered, sounding very relieved. "You've found the Darke Disguise."

The Darke Disguise reminded Septimus of one of Sarah Heap's floaty scarves, although Sarah favored brighter colors. This was an indeterminate color that Sarah would have condemned as dull; it was also much larger than any scarf that Sarah possessed. Septimus kept on pulling it from the tinderbox, and the Darke Disguise kept on coming, falling in fine, weightless folds across his lap, tumbling down to the floor. Septimus began to wonder how long it actually was.

Marcellus answered his unspoken question. "Its length will be right for whatever you need. Now, Apprentice, a word of advice. I suggest you pull a thread from it now - it is easily done - and keep it with you. It will be as strong as a rope and, in my experience, it can be useful to have something a little Darke that comes easily to hand when one is venturing into these realms."

Not for the first time, Septimus wondered what secrets Marcellus had in his past. But what he said made sense. He pulled a thread from the loose weave and began to wind it into a neat coil.

Marcellus looked on approvingly. "Confidently done. Remember, the Darke power of this exposed thread will begin to evaporate after about twenty-four hours. Do not keep it in your Apprentice belt; you do not want to upset any Charms or Spells. A pocket will do."

Septimus nodded - he'd figured that out for himself.

"Now I suggest you return the Darke Disguise to the tinderbox," said Marcellus. "Any time spent out, even in here, dilutes its power a fraction."

As instructed by Marcellus, Septimus spoke the words "I knaht uoy, esaelp eriter," and the Darke Disguise evaporated into the tinderbox like a wisp of smoke.

Marcellus regarded his Apprentice with satisfaction. "Very good indeed. It obeys you well. Just before you enter the Darke Portal, open the box and instruct it so - 'ehtolc Sum.' Now that it Knows you it will stick to you like a second skin. Take care not to wear it away from the Darke, as it will soon dissolve into nothing, which is why I have to show it to you in this chamber. Use it well."

Septimus nodded. "I will," he said.

"And one last thing."

"Yes?"

"The Darke Disguise may corrupt Magyk. Do not take this box into the Wizard Tower."

Septimus was dismayed. "But . . . what about my Dragon Ring?"

"You are wearing the ring. It is part of you, and the Darke Disguise will protect all parts of you." Marcellus smiled. "Do not worry, it will shine as brightly as ever for you, Apprentice, although others will not see it."

Septimus looked at his ring, which was glowing in the gloom of the SafeChamber. He was relieved. He would feel lost without it.

Marcellus issued his last instruction. "When you return with Alther - as I know you will - you must bring the Disguise straight back here to store it. Understand?"

"I understand," said Septimus. "Thank you. Thank you very much, Marcellus." Carefully he put the tinderbox in the deepest, most secret pocket of his Apprentice tunic. "I'll see you later. At the party," he said.

"Party?" asked Marcellus.

"You know - my birthday party. With Jenna. At the Palace."

"Ah, yes. Of course, Apprentice. I forget."

Septimus rose to go. This time Marcellus Pye did not stop him.