Septimus decided to take the Outside Path along the Castle walls, just in case Marcia had been suddenly called out on Magykal business, headache and all - it would be just his luck to bump into her. With mounting excitement, he picked his way through the boatyard, careful not to make any noise that might disturb Jannit. Soon he reached the upside-down hull of an old river barge, and squeezing behind the barge, he found what he was looking for - the steep steps that led up to the Outside Path.

The Outside Path was a narrow and crumbling ledge just a few feet above the dark water of the Moat. It had not been built as a path, but was the point at which the huge foundations of the Castle walls finished and the slightly narrower walls, which were built from smaller, more finely cut rock, began. When Septimus had been in the Young Army, many of the older boys had run along the Outside Path for a dare, but it was not something that Septimus had ever wanted to do - until now. Now, with the confidence of a year and a half as the ExtraOrdinary Apprentice and the knowledge that if he slipped and fell he could always use his Flyte Charm, Septimus climbed the steps up to the Path.

The Path was narrower than he had expected; Septimus walked slowly, placing one foot in front of the other and feeling for loose stones as he went. He was grateful for the light of the waning full moon, which reflected off the Moat and shone on the pale stone of the Castle walls, making it easy to find his way. The air was calm in the lee of the east wind, and although Septimus could see the tops of the trees swaying, it was still and quiet beside the water.

Far away on the other side of the Moat, frighteningly near the Forest, the lights of the Infirmary flickered as the branches of outlying Forest trees moved in front of the long line of tiny, candlelit windows. Septimus stopped and watched the steady progress of Sarah Heap's lantern across the Moat as Nicko rowed toward the Forest bank. The lantern seemed such a small pinpoint of light against the great expanse of dark trees. He hoped that Alther would be waiting for her when they reached the Forest side.

Some minutes later, the lantern reached the far bank and Septimus saw Alther's shape illuminated in the glow. Relieved, he set off once more. Soon the curve of the Castle wall took him out of sight of the Infirmary, and a long empty stretch of the Outside Path lay before him. Septimus was a little surprised that he could see no sign of Snake Slipway. He had not realized how much the Castle walls curved. He was used to taking the direct route to the Slipway, but he pressed on, the thought of being able to talk to Marcellus Pye keeping him going.

As Septimus continued - more slowly than he would have liked, for the Path was very uneven - he could feel the chill coming off the Moat and smell the dankness of the water as it flowed by sluggishly. A layer of mist was beginning to form just above the Moat, and as Septimus watched, it grew thicker until he could no longer see the surface of the water. A soft silence came with the mist, which was broken only by the occasional moan of the wind in the tops of the trees on the outskirts of the Forest.

His enthusiasm for seeing Marcellus Pye began to wane, but Septimus kept going. He had no choice, for the Outside Path had now become so narrow that it would have been treacherous to turn around. After slipping twice on some loose stones and very nearly tumbling into the Moat below, Septimus decided that he was being foolish trying to walk along the Outside Path. He stopped, leaned back against the walls to try to keep his balance and fumbled in his Apprentice belt for his Flyte Charm. His hand got stuck in the small pocket in which he kept the Charm, and as he tried to pull it out, Septimus felt himself falling forward. In a panic, he grabbed at the stones behind him and only just managed to pull himself back up.

By now Septimus knew that taking the Outside Path was a stupid mistake, but he made himself concentrate on the way ahead and tried to pay no heed to the thoughts that clamored for his attention. These were:

His warm and comfortable bed, which was waiting for him at the top of the WizardTower.

The moaning of the wind in the tops of the trees.

Why did the moaning sound so weird?

His bed.

Did wolverines come down to the Castle walls at night?

Could wolverines swim?

They could, couldn't they?

His bed.

Why did the mist seem so spooky?

What was under the mist?

Do wolverines especially like swimming underneath mist?

His bed.

Hang on ... didn't Marcellus Pye's writings say he had found the secret of eternal life?

Suppose Marcellus wasn't just a normal old ghost?

Suppose he was a five-hundred-year-old man? Wouldn't he just be a skeleton with bits of skin hanging off?

Why hadn't he thought of this before?

It was then that a large storm cloud covered the moon and Septimus was plunged into darkness. He stopped dead, his heartbeat pounding in his head, and pressed himself against the wall. As his eyes got used to the dark he found he could still see the tops of the Forest trees, but he could not, for some reason, see his feet, however hard he stared. And then he realized why. The mist had risen and was covering his boots; he could smell its dampness. The Dragon Ring on the index finger of his right hand was shining with its comforting soft yellow light, but he took the ring off and put it in his pocket, for suddenly the glow of the Dragon Ring felt like a large label saying, "Come and get me."

It was probably only about half an hour later - although by now Septimus was sure it was at least three nights strung together by a Reverse Enchantment - when he heard footsteps behind him. Heart in his mouth, Septimus stopped, but he did not dare turn around for fear of falling into the Moat. The footsteps continued toward him and Septimus set off again, stumbling along the Path, peering into the night, desperate for the sight of Snake Slipway, but storm clouds kept piling in and the moon stayed hidden.

The footsteps were light and sounded agile, and Septimus knew they were gaining on him, for every two steps he managed to take, the Thing - and he was sure it was a Thing - took three. Desperately, Septimus tried to pick up speed, but still the footsteps kept coming.

Suddenly Septimus heard a noise behind him. "Ssss ... sssss..." The Thing was hissing at him. Hissing. It must be a SnakeHead Spectre ... or even a Magog. Magogs sometimes hissed, didn't they? Maybe one of DomDaniel's Magogs had got left behind, maybe it lived in the Castle walls and then it came out at night when some idiot decided to go for a stupid walk along the Outside Path.

"Sssss!" A loud hiss sounded in his ear. Septimus jumped in fright. His right foot slipped from the narrow, crumbling Path and he slid off, hands clutching frantically at the stones as he went. His right boot was already in the Moat and Septimus was about to follow it when something grabbed his cloak.