Night drew on in the room behind the Big Red Door. The red glow from the embers in the fire threw a warm light over the sleeping figures swathed in blankets. Outside a northeast wind began to blow and rattle the windowpane. One of Sarah's dreams began to turn into a nightmare.

"Ethel!" she gasped, sitting bolt upright.

"Ah! You all right, Mum?" asked Simon, who was taking his turn on watch and had been drifting into a doze.

Sarah wasn't sure. "I dreamed . . . I dreamed I was being suffocated. And then poor little Ethel . . . oh, Ethel."

Simon was suddenly on his feet. A tiny tendril of smoky Darkenesse was curling in under Benjamin Heap's door.

"Wake up! Everyone wake up!" he yelled.

Thunder whinnied loudly and snorted. Instantly everyone was awake.

Septimus made for the door, intending to put some kind of Emergency Stop on it. But Marcellus grabbed him.

"Do not touch it, Apprentice! It is too dangerous - and too late."

Septimus stopped. Another wisp of Darkenesse puffed in around one of the hinges - it was indeed too late.

Jenna appeared at her cupboard door, hair awry, witch's cloak up to her chin against the cold. "What is it?" she asked sleepily, half knowing already what the answer was.

"It's coming in," said Septimus. As if on cue, a spurt of Darkenesse puffed through the keyhole with such force that it looked as though it had been blown in with a pair of bellows.

"We must leave at once," said Marcellus. "Sarah, is everything ready?"

"Yes," said Sarah sadly.

As part of the previous day's preparations, a huge coil of rope lay on the floor below the window. One end of the rope was tied around the central mullion of the window; it then snaked back across the room, looped around the base of the huge stone chimney that went up through the middle of the room, where it was secured with an impressive knot. Sarah pulled open the window and a freezing blast of air blew in, taking her breath away. It was not a night to be out, let alone a night to be climbing nearly a hundred feet down an exposed north wall, but they had no choice. With Jenna's help Sarah picked up the coil of rope and together they heaved it out the window into the night. They jumped back and watched the loop around the mullion tighten as the rope hurtled down to the river far below.

Simon went over to Thunder. "Good-bye, boy," he whispered. "I'm sorry . . . so sorry." He put his hand in his pocket and felt for his last peppermints. Thunder nuzzled at his hand and then rubbed his nose against Simon's shoulder. Breaking his promise to Lucy not to do any more Darke stuff, Simon did a Sleep Spell laced with just enough Darke to give Thunder a chance of surviving. As the horse settled down onto Sarah's best rug and his eyes closed, Simon gently placed a blanket over him.

The previous day, when they were making plans to escape, they had decided to leave in order of their importance to the safety of the Castle. That had made Simon third to last - Sarah had been next and then Lucy had been last, but Simon had insisted on going last. There was no way he was going to leave Lucy and his mother alone to face the Darke. As Septimus and Marcellus stood at the window, Simon sat beside Thunder and wondered if they would be spending their time together in the Darke Domaine.

Another smoky tendril came slithering under the door.

"Time to go, Apprentice," said Marcellus.

Septimus steeled himself. He took a deep breath and looked down. He saw the rope snaking down the rough stones of the Ramblings wall and disappearing into the night. The previous afternoon he had Transformed it from three rugs, two blankets and a pile of old towels. He had never Transformed anything into something so continuous before and, as he peered out the window and tried - unsuccessfully - to see the ground, he hoped he'd done it right.

Sarah was fussing, anxiously checking the knots. She was confident that even if the mullion did not hold their weight, the chimney would - but she was not so sure about the knots. She just hoped she'd got them right. If only Nicko was here, she thought, he'd know how to do them. A pang of concern shot through her at the thought of Nicko, but she pushed it away. Time enough to worry about Nicko when they'd all got out safely, she told herself.

"I'll just Call for Spit Fyre one more time," said Septimus, putting off the terrifying moment of climbing out.

Marcellus glanced anxiously back at the door. A long stream of Darke Fog was curling beneath it and creeping across the floor toward the fireplace.

"No time now," said Marcellus. "Do that when we've got down there."

Shakily Septimus took hold of the rope. His hands were clammy but he had made the rope rough and thick for a good grip. He climbed up onto the windowsill and as he swung his legs over the side, Septimus felt a shiver of vertigo run through him - there was nothing between his feet and the river far below.

"Be careful, love," said Sarah, raising her voice against a sudden gust of wind. "Don't go too fast - far better you get down safely. When you've got to the bottom, give the rope three tugs, then Jenna will go."

With his arm around his Sleeping horse, Simon watched his youngest brother inch out into the night until all he could see were Septimus's hands gripping the rope and his curls blowing wildly in the wind.

Septimus began his descent. He knew that to give everyone a chance of getting out he had to put his fear of heights to one side and concentrate on getting quickly down the rope. It was not easy. The wind kept pushing him against the wall, banging him against the protruding stones, taking his breath away and disorientating him. It was only when - terrifyingly - his grip slipped and he found himself almost at right angles to the wall that Septimus discovered that if he deliberately leaned out from the rope, the wind buffeted him less and he could almost walk down the rough stones, many of which stuck quite a long way out and gave good footholds.

Septimus's descent continued until he stepped on the bush that had saved Stanley. The sudden change of foothold panicked him and he very nearly let go of the rope. But as he steadied himself and got his breath back he realized he could smell the river and hear the lapping of water. He speeded up and soon, like Stanley before him, he had landed on the mud. He gave three quick tugs of the rope and leaned against the Ramblings wall, shaking. He had done it. He felt the rope move in his hands and knew that Jenna was on her way down.

It was not long before Jenna landed beside him, breathless and exhilarated. Unlike Septimus, she had loved the excitement of the descent. They stood, looking up to the only lighted window in the entire Ramblings wall and saw another figure climb out. The figure moved quickly down, and Septimus was surprised at how agile Marcellus was - but a scream when the figure met the spiky bush growing from the wall told them it was Lucy, not Marcellus as they had all agreed earlier.

"He made me go first," said Lucy breathlessly, as she tugged the rope. "He said he'd lived long enough already. And he said Simon must come next."

"Simon!" spluttered Septimus. "But we need Marcellus."

Lucy said nothing. She looked up and did not take her eyes off Simon as he descended the rope, fast and easily. Soon he was beside them. Quickly he gave the rope three tugs and looked up anxiously at the window.

"The door's not going to hold much longer," he said. "They're going to have to get a move on."

It was too much for Jenna. She had waited once for her mother outside a room filling with Darkenesse and once was enough. She couldn't stand the thought of doing it again.

"Mum!" she called up. "Mum! Hurry up! Please, hurry!"

But no one came.

Up in the room behind the Big Red Door, two people who should have known better were arguing about who was leaving next. Sarah looked around the room she loved - that she now knew Silas loved too - and she dithered. No matter that Benjamin Heap's door was changing as she looked at it, the red paint blackening as though a fire was raging on the other side. No matter that wisps of Darke Fog hung in the room like storm clouds heralding the arrival of a hurricane - Sarah would not budge. She was determined to be the last to leave.

"Marcellus. You must go first."

"I will not leave you here alone, Sarah. Please, go."

"No. You go, Marcellus."

"No. You."

It was Benjamin Heap's door that settled it. There was a sudden craaaaack. A panel split and a long stream of Darkenesse poured in. In a moment the fire in the hearth was out.

"Oh, that poor horse," said Sarah, still dithering.

"Sarah, get out," said Marcellus. He grabbed her hand and pulled her to the window. "We both go," he said.

Sarah gave in. Surprisingly agile, she clambered out of the window and swung herself onto the rope - she had not lived in Galen's tree house for nothing. Marcellus followed. He slammed the window shut, jamming it on the rope. Then he, too, easily began the descent, which was nothing compared to the tall chimney in the Old Way that he had regularly climbed in his old age. Far below Septimus, Jenna, Simon and Lucy looked at each other in relief.

Sarah and Marcellus made good progress, slowed only by Stanley's bush, which Sarah irritably kicked at. It was the last straw for the bush, and it went tumbling in a shower of stones, which scattered the watchers below. When they looked back up, the light in the small mullioned window had gone out. The great rock face wall of the Ramblings was now completely in Darkenesse.

At last Sarah stepped unsteadily onto the ground. Jenna flung her arms around her.

"Oh, Mum."

Marcellus pushed away from the wall and jumped athletically - he hoped - away from the knot of people gathered around Sarah. He landed with a splat. "Eurgh," he muttered. "Wretched horse."

"You only just made it," Septimus told him disapprovingly. He thought Marcellus should have stuck to the agreed order of leaving.

"Indeed," said Marcellus, inspecting his ruined shoe.

Marcellus's casualness annoyed Septimus. "But we decided the order we would leave for a reason. It was important - for the whole Castle," he persisted.

Marcellus sighed. "But things that are right in the cold light of reason may feel very wrong when faced with reality. Is that not so, Simon?"

"Yes," said Simon, remembering the Thing strangling Sarah. "Yes, it is."

"It's my fault," said Sarah. "I wanted to be last - like a captain leaving her ship. Anyway, it doesn't matter; we're all safe now."

"It doesn't feel very safe," said Lucy, saying what most of them were thinking. She looked at Jenna accusingly. "You said there were always boats here. But I can't see any."

Jenna looked along the strip of mud that ran between the edge of the river and the sheer walls of the Ramblings. She didn't understand it. There were always little boats tied up on the numerous outhauls - lengths of rope that snaked out from rings in the walls to weights sunk onto the riverbed. But now there were none.

Lucy was getting agitated. "What are we going to do? The water's coming up and I can't swim."

"It's okay, Lucy," said Septimus, sounding more confident than he felt. "I'll Call for Spit Fyre now. He'll probably come now that we're away from the Darke."

Septimus took a long, deep breath and gave the loudest dragon Call he had ever made. The piercing, ululating sound bounced off the Ramblings walls and echoed across the river, and as the last faint whispers died away, his Call was answered - not by the hoped for sound of dragon wings beating the air, but by the answering cry of a monster within the Castle.

"Sep . . . what have you Called?" whispered Jenna.

"I don't know," whispered Septimus in reply.

Spit Fyre did not come, and Septimus dared not Call again.

The thin strip of mud between the sheer walls of the Ramblings and the broad band of the deep, cold river was a temporary refuge only. They knew that as the tide came in it would slowly disappear. They gazed longingly over to the safety of the opposite bank. Far away to the right, flickering through the bare branches of the winter trees, were the distant lights of a farmhouse. Upstream to the left was glow of firelight in the downstairs window of the Grateful Turbot Tavern. Both were unreachable.

"We'll have to walk down to Old Dock," said Septimus. "See if we can find a boat there."

"One that isn't half sunk already," said Jenna.

"Do you have any better ideas?" demanded Septimus.

"Stop it, you two," said Sarah. "I don't think anyone does have any better ideas - do we?"

There was silence.

"Old Dock it is," said Sarah. "Follow me."

Sarah led the cold, tired group along the mud. But whereas Stanley, with the lightness of a rat, had scampered over the top of the mud, it was not so simple for humans. Their feet sank deep into the goop and they stubbed their toes on hidden rocks and tripped over the empty outhauls. As they struggled on through the freezing mud, they saw countless open windows from which abandoned knotted sheets and makeshift ropes dangled - and they now understood why all the boats had gone. Even the floating pontoons had been unhitched and pressed into service; there was nothing left afloat on their side of the river.

Finally they arrived at the Underflow, an underground stream that ran from below the Castle. Sarah, not realizing where she was, took a step forward into the dark and fell into deep, fast-flowing water.

"Agh!" Sarah gasped with shock as she was swept out into the river.

There was a loud splash and a scream from Lucy. Simon surfaced in the river, spluttering - then he turned and swam into the darkness after Sarah.

"Simon!" yelled Lucy. "Aaaaaaaaaaaaaaaaagh! Simon!"

Jenna, Septimus, and Marcellus stood, shocked, on the muddy bank of the Underflow. They stared into the night but could see nothing. Lucy stopped screaming, and the sounds of Simon swimming receded. Chilled by the freezing wind, they listened in silence to a few faint splashes coming from somewhere in the middle of the river.