Jenna couldn't sleep. Not because of the icy chill of the cell air, or because of the hard little bed, the thin scratchy blanket or because her clothes felt cold and damp. She could not sleep because of the thought of the skull staring empty-eyed at her door. Whenever she closed her eyes an image of the grinning white skull drifted by and woke her with a start.

Jenna gave up trying to sleep. She wrapped herself in Lucy's cloak, her mind racing as she went over the events of the day. Until she had seen the skull, Jenna had found it hard to believe that Simon meant her any harm. In her mind he was still her eldest brother, the reliable one who always helped her out when she was in trouble and showed her how to do her homework. But that was before Simon had picked up the skull, cradled it in his arms and told her how he had rescued DomDaniel's skeleton from the Marram Marshes on the night of the Apprentice Supper and that he was now DomDaniel's Apprentice. "How about that, little Miss Princess? And unlike his last useless Apprentice, I am carrying out his every wish to the letter. And his very particular wish was to have the Castle free of any interfering royalty, such as yourself. He considers the power of the Queen an intolerable imposition on any ExtraOrdinary Wizard. As do I. So, if we want some proper Magyk back in the Castlenot just Marcia's dinky little spellsthen someone has to go." Simon had looked at her with a horrible coldness in his eyes, which stayed with her still.

Jenna sat on the edge of the bed, thinking. She wondered why Simon hadn't already got rid of her. He could have easily pushed her off the ravine into the river or just left her out for the Land Wurms. But Jenna already knew the answer. Whatever Simon might have said, he had still wanted to show off to his little sister. But he had done that now, and tomorrow it would be a different story. Maybe tomorrow he would leave her out for the Land Wurmsor the Magogs.

Jenna shivered. She heard a low noise drifting through the wall and her heart leaped into her mouth. It was a strange, regular,snorting noise, and she knew what it wasit was the skull. The noise got louder and louder; Jenna pressed her hands over her ears to blot out the awful sound, and then suddenly she realized what it really was: Simon was snoring. Which meant that Simon was asleep and she was awake. She could try and escapeshe must try and escape.

Jenna tried the iron door. It was bolted but there was a small gap between the door and the wall, and Jenna wondered if she could push something through the gap and somehow undo the bolts. She looked around the cell but Simon had not been so considerate as to leave her a hacksaw. Jenna put her hands in her pockets, wondering if she had anything on her that could help. Septimus would have the very thing, she thought. He always carried his Young Army knife, which had about a hundred and one different uses, mostly involving horses' hooves. She missed him.

The thought of Septimus made Jenna remember the chocolate Charm he had given her that morning. Where had she put it? There it was, damp and sticky, stuck at the bottom of her tunic pocket. She pulled out the Charm, held it in her palm and squinted at the inscription:Take me, shake me,and I will make thee:Quetzalcoatl's Tchocolatl.

Well, she thought, it was worth a try.

Jenna tried to remember what Septimus had said when he had told her how to use the Charm. She cupped both of her hands together and shook the Charm up and down as hard as she could to Activate it. As she did so, she whispered the words written in the small brown square and concentrated all her thoughts on what she wanted. Sure enough, the Charm began to work. It grew warm and smooth in her cupped hands, as though it were a real piece of chocolate. Then, just as Septimus had said it would, it began to buzz like a small fly trapped in her grasp. Jenna waited until the Charm was almost too hot to hold, and then quickly placed it on the object she wanted to turn into chocolatethe door of the cell.

Jenna did not really believe that Septimus's Charm could turn a thick iron door into chocolate. But, as she pushed the Charm against the door, to her amazement she felt the hard pitted metal change into a smooth surface that was cool, rather than icy cold, to the touch. Something else had changed too. Jenna sniffed the airthe cell was filled with the faint smell of cocoa.

Hesitantly, Jenna took the Charm off the cell door. The Charm was cool now; she slipped it back into her pocket and gazed at the door. At first Jenna thought it seemed much the same as it had before, except now, as she looked more closely, she could see that the rusty hinges and even the flap over the keyhole were beautifully molded in chocolate. Never in her life had Jenna seen so much chocolate and, unfortunately, never had she felt less like eating it.

Jenna soon discovered that a massive slab of three-inch-thick chocolate, chilled hard on a cold night, is not easy to shift. She pushed as hard as she could against it but the slab stayed as firm as if it were still iron. She decided to start scraping some shavings off the door to make it thinner, but it was hard work and she thought it would take all night.

Jenna sat down disconsolately on the edge of the bed and ate some of the shavingsit was extremely good chocolate, even better than the Choc Chunks from the sweetshop at the end of Wizard Waywhile she wondered what to do. After a few minutes the chocolate began to help her think more clearly, and Jenna realized that she needed to find something sharp to help cut a hole in the door. Simon had made sure that there was nothing sharp in the cell, but, as Jenna hunted around, she soon discovered that even Simon did not think of everything. He had forgotten about the bedsprings.

Jenna threw the thin mattress off the bed and quickly unwound one of the looser bedsprings until she held a sharp, pointed piece of metal in her hand. Then she set to work, scraping away a hole in the door big enough to squeeze through, while, to her relief, Simon's snores carried on reverberating through the walls.

An hour later, Jenna's bedspring had cut a large rectangle at the bottom of the door. All she had to do was give it a push and hope that it did not fall over with too loud a thud. Carefully, Jenna pushed against one edge of the rectangle and to her delight, it moved easily. Very quietly, Jenna laid the thick slab of chocolate on the floor, and, in case she got hungry later, she broke off the keyhole cover and stuffed it into her pocket. Then she squeezed through the opening, stood up and wiped her chocolaty palms on her tunic.

Simon was still snoring loudly; the snores echoed around the circular chamber and were strangely comforting, for at least they were human. Jenna tiptoed past the huge white dish of the Camera Obscura, glancing down for a last look at the strangely compelling scene outside, and noticed that Simon had left the Enlarging Glass lying on the dish. Jenna picked up the Glass and stuffed it into her tunic pocket. Now Simon would not find it so easy to see where she had gone.

Next, Jenna found the Glo Grub Tub; Simon had not replaced the barrel lid properly and a bright yellow light shone from the gap. The Glo Grub Tub was a large wooden barrel, full almost to the brim with hundreds of thousands of tiny Glo Grubs wriggling around. Jenna took a Glo Lamp from a neat line of empty lamps placed next to the barrel, picked up the scoop and filled the glass tube with squirming Glo Grubs. Jenna did not like using Glo Lamps, but she had no choice. Sarah Heap refused to use them because once the grubs were put in a lamp they did not live longer than a few hours. It was, Sarah said, a terrible thing to kill so many creatures just for a person's own convenience. Sarah used good old-fashioned candles.

"I'm sorry, grubs," Jenna whispered as she scooped them up.

Jenna filled the lamp and left the lid of the Glo Grub Tub open to give the grubs a chance to escape. She raised the lamp and,for the first time, she really saw the place that Simon Heap had made his own.

The Observatory was a huge round chamber. The walls, roughly hewn out of the solid slate mountain, sloped upward and inward until they met at the lens for the Camera Obscura. A thick milky slab of glass set into the roof let in the moonlight, and Jenna realized that most of the Observatory was below ground. Silently, she crept past the metal Thunderflash Chamber and past neatly ordered shelves containing piles of Darke books, Reverse Conjurations, Hexes and Curses. She averted her eyes from a sinister-looking collection of flasks in which she could see misshapen creatures dimly floating in a yellow liquid. Every so often a bubble of gas rose from the bottles and filled the air with a foul smell. In a distant corner a small glass-fronted cupboard glowed with a dull blue light. It was fastened with an impressive array of bolts. Inside, coiled up, lay a small black snake.

Simon Heap's snores reverberated through a large wooden door, which he had painted purple and covered with Darke symbols. Jenna passed the door and as she did so she trod on Sleuth. Somehow Jenna managed to change her scream into a strangled squeak, but Simon's snores stopped. Jenna froze, holding her breath. Was he awake? Should she run while she had the chance? Would he hear her footsteps? What should she do? And then, to her horror, Sleuth began bouncing on the spot. With each bounce a soft thud echoed around the Observatory. In a flash, Jenna scooped up the ball and a few seconds later Sleuth had been pushed deep into the contents of the Glo Grub Tub. Jenna closed the lid, snapped the lock shut and apologized to the grubs for the second time that night.

Muttering the Protection Spell that Marcia had taught her some time ago, Jenna crept past the ever-watchful skull, wondering what Simon had done with the other bones. As she went by she was sure that deep inside the skull a pair of eyes was watching her. She dared not look.

Once past the skull, Jenna ran. She tore through the archway and raced down the steep steps as fast as she could, as though DomDaniel himself were chasing her. Every now and then she glanced behind just to make sure that he wasn't.

When she reached the foot of the steps, Jenna stopped and listened for footsteps. There were none. Her spirits lifting a little, she took a step forward. Her feet shot out from underneath her and she came crashing to the ground. The Glo Lamp leaped out of her hand, scattering Glo Grubs across the ground. Jenna scrambled back to her feet and brushed off her tunic. Magog slime. A shudder of nausea passed through her, followed by a feeling of panic. Quickly she gathered up as many Glo Grubs as she could find, and, holding them in her cupped hand, she moved fast and silently along the tunnel toward Thunder's stable.

Jenna reached the Wurm Chamber safely, with no telltale swish of a Magog behind her. Thunder was standing quietly it his manger, chewing on the hay that Simon had left for him. He looked up as Jenna emerged from the tunnel.

"Hello, Thunder," she whispered. Thunder glanced at Jenna for a moment and then turned his attention back to tne hay.

Good, thought Jenna, he remembers me. She walked slowly to the horse and patted his mane. It seemed cruel to take him out again into the cold night air, but she had no choice. She took the bridle off its hook and very gently approached Thunder. The horse didn't seem keen; he shook his head and snorted noisily.

"Shh," whispered Jenna. "Shh, Thunder. It's all right. It is."

She patted his nose gently and then reached into her tunic pocket for the chocolate keyhole cover and offered it to him in her outstretched palm. Thunder nibbled at it delicately and looked at Jenna with a faintly surprised air. Jenna was quite sure that Simon never gave his horse chocolate. And quite right too; she never gave her horse chocolate either, but sometimes bribery was the only option.

With the hope of more chocolate, Thunder allowed Jenna to put his bridle on and saddle him up again. Jenna was just about to lead the horse out when she thought of something. She scooped up a handful of pebbles from the ground and, using the Cnarm again, she turned them into chocolate. Then Jenna stuffed most of the chocolate pebbles into her pocket, keeping one to wave under Thunder's twitching nose.

"Come on, Thunder," she coaxed softly, "come on, boy, let's go."