Nicko had set off to rescue Jenna and her companions from the Ramblings as soon as Stanley had left. He had not wanted to take the Port barge but he'd been outnumbered - even Jannit had agreed with Rupert and Maggie. She had told him that the Heaps were not the only ones to need rescuing; there would be others, surely, and they must take the biggest boat they could. Besides, what else did they have that was suitable? It was the depths of winter. Most of their boats were out of the water and sitting on props in the boatyard. Nicko had agreed reluctantly but before long he was regretting his decision. The Port barge - or the Pig Tub, as he soon began to refer to it - was nothing but trouble.

Right from the beginning progress had not been easy. They had to go the long way around because, for the Port barge, the Moat was not navigable past the boatyard. Added to that, the wind was against them and the long, unwieldy boat, which could not easily sail in the narrow confines of the Moat, needed to be poled along by Rupert and Nicko. This involved them standing on either side of the barge, pushing long barge-poles through the water. Progress was made a little easier by the falling tide, which was flowing their way, but it was still painfully slow and gave them plenty of time to stare at the Darkened Castle.

"It's like everyone has . . . gone," Maggie whispered to Rupert, not liking to say "died," which was what she meant. She didn't see how anyone trapped in the Castle could survive and thought that the sooner she and Rupert got away to the Port, the better.

Nicko had pushed the oar through the water with all his might, propelling the barge inch by frustrating inch toward Raven's Rock, longing for the moment when they were out in the wide river with the wind in their sails. And then, just before the Moat joined the river, they ran aground on the Mump - the notorious mudbank at the entrance to the Moat. Nicko couldn't believe it.

Despite desperate efforts with the grounding poles, made specially to push a barge off a mudbank, nothing they could do would shift the "stupid Pig Tub idiot boat," as Nicko put it. She was stuck fast.

Maggie was horribly embarrassed. A skipper going aground was hard to live down. At least she did not have a boat full of passengers and livestock with whom she would be marooned for six interminable hours, enduring their complaints, moans, barks and brays with no means of escape. With any luck, no one would get to hear of this. And Port barges were made to sit on mud, so there was no harm done.

But for Nicko and Rupert, there was harm done. They stared disconsolately over the side at the thick, muddy water, knowing that every minute marooned on the mudbank meant another minute of danger for Jenna, Sarah, Septimus and Lucy (they had forgotten about Marcellus, and neither of them cared if Simon was in danger). Although neither said it, Nicko and Rupert had no idea if they were even still alive. All they had was hope, which faded as the tide fell.

And then they had nothing to do but sit and stare at the Castle - and try not to think about what creature could be making the spine-chilling roar that echoed across the Walls every now and then and made the hairs on the backs of their necks stand on end. The only consolation was that, from where they were stranded, they could now see the indigo and purple glow of what Nicko told Rupert must be the Wizard Tower SafeShield.

At midnight, down in the Port, the tide turned. Salt water began to creep into the empty gullies in the sand and it began to rise once more in the sleeping harbors and push its way back up the river. At about three in the morning the Port barge shifted. To the accompaniment of another spine-chilling roar from inside the Castle, Nicko and Rupert got out the grounding poles and pushed with all their strength, knowing that this time they would get free. Ten minutes later they were sailing - slowly - toward the river. According to Jannit they were a little too close to Raven's Rock; Maggie pushed the huge tiller across to the right, but the boat seemed sluggish - and as they sailed beneath Raven's Rock they hit something.

Jannit knew at once that they'd hit one of the Beaks - a line of small rocks that came out from Raven's Rock and were not visible after midtide. Maggie was distraught. It didn't help that Jannit had said she'd told her they were going too close and that Maggie had snapped she knew that, thank you, Jannit.

Rupert and Nicko took a spare sail and rushed below. Water was pouring into the cargo hold; Rupert was horrified, but Nicko knew that water coming in often looked worse than it really was. He and Rupert rammed a heavy canvas sail into the gash in the hull and found to their relief that the hole was barely bigger than Rupert's fist. The gush stopped and the red sail darkened as it grew wet. The water still came in but slowly now, dripping from the canvas at a speed that allowed Nicko and Rupert to bail it out with a bucket.

A holed boat must be got to shore as soon as possible. They decided to take the Port barge to the nearest landing stage on the Castle side - no one wanted to risk tying up on the Forest side at night. While Rupert and Nicko poured buckets of river water over the side, Maggie and Jannit, both pulling hard on the unusually stiff tiller, took the barge across to the Palace Landing Stage. As they got closer they saw that the normally brightly lit Palace - a landmark for returning mariners - was utterly dark.

"It's as if it isn't there anymore," whispered Jannit, staring across to where she knew the Palace should be and seeing nothing but blackness.

By the time they drew near to the Palace Landing Stage -  which, unlike anything behind it, was still visible - everyone was having second thoughts about the wisdom of getting any closer. Nicko shone one of the powerful boat lanterns across to the bank but he could see nothing. The light petered out just behind the landing stage on what looked like a fog bank, but different. Fog had a brightness to it and bounced light back. This Fog drew in the light and killed it, thought Nicko with a shiver.

"I don't think we should get any closer," he said. "It's not safe."

But Maggie, worried about her boat sinking, didn't think the river was exactly safe either. She pushed the tiller hard to the right - the barge was being particularly contrary - and headed for the landing stage.

Suddenly a ghostly voice drifted across the water.

"Beware, beware. Come no closer. Flee . . . flee this place. This terrible place of doooooooom."

White-faced in the light of the lantern, they looked at each other.

"I told you," said Nicko. "I told you it wasn't safe. We have to go somewhere else."

"All right, all right," snapped Maggie, who no longer had any confidence in her own decisions. "But where? It's got to be close. Supposing everywhere is like this - what do we do then?"

Nicko had been thinking. He knew from Stanley that this was a Darke Domaine. Nicko hadn't taken much notice of his Magyk classes at school - in fact, as soon as he was old (and brave) enough he had cut them to go to the boatyard - but he did still remember a few Magykal rhymes. The ones he thought of were:

A Darke DomaineMust remainWithin the bounds of water.

and:

The Castle Walls are tall and stout,They are built to keep the Darkenesse out.But if the Darkenesse grows within,The Castle Walls will keep it in.

"Everywhere won't be like this," said Nicko in answer to Maggie's question. "This Darke stuff is stopped either by the water or by the Castle Walls. That's why we were all right in the boatyard, because we're outside the walls. So I think if we go up to Sally Mullin's place we'll be okay; she's outside the Castle Walls. We can tie up at the New Quay just below Sally's pontoon and we'll be safe. Then Rupert and I can find another boat. Okay?"

Maggie nodded. It was as okay as anything was likely to be right then - which was not, in her opinion, saying a lot. But she and Jannit set the sails and turned the Port barge out into the river.

It was then that they discovered that the rudder was jammed. The barge had not escaped unscathed from being grounded; it now insisted on turning steadily right, which was probably why she had hit the Beaks, Maggie realized. The barge now refused to turn left up to the New Quay. To everyone's dismay, it drifted inexorably into the Raven's Rock Run until it was taken by the reverse current and pulled through the deep, choppy waters at the base of the rock so that it was now heading rapidly away from the Castle. Desperately they tried to steer out of the Run using the barge oars as rudders, to no avail. The Pig Tub made a beeline for the Forest and as they neared the overhanging banks tangled with trees, they began to hear the frightening grunts and screeches of the Forest night creatures. But at least, Nicko pointed out, they could hear something normal. It was better than the awful silence of the Castle punctuated by that weird roar.

They were lucky. Once more they ran aground, this time on a shingle bar some yards out from the bank, which left a comfortable stretch of water between the barge and the Forest. Maggie, at her insistence, kept watch. "I'm skipper," she said firmly when Rupert objected. "Besides, you three will be busy working on the rudder tomorrow. You need to sleep."

Nicko, Rupert and Jannit spent most of the following day fixing the rudder. It would have been a quick and easy job in the boatyard, but without the right tools it took much longer. It was also much wetter and colder than it would have been in the boatyard, and even Maggie's steady supply of hot chocolate did not stop tempers fraying by the afternoon.

The winter sun was low in the sky when the repaired Port barge finally floated off the shingle bank and headed upriver toward the New Quay. As the barge rounded Raven's Rock they saw the Darkened Castle in daylight for the first time. It was a shock. At night the only visible sign of the Darke Domaine was the absence of the normal nighttime lights, but the daylight showed the full scale of the disaster that had overwhelmed the Castle. A great black dome of cloud squatted within the Castle Walls, obscuring the usual cheerful sight of the higgledy-piggledy rooftops and chimneys and the occasional turret or tower that would greet any boat as it rounded the bend at Raven's Rock. It was, thought Nicko, like a dark pillow pushed onto the face of an innocent sleeper. But still, shining above the Fog - just - like a brilliant beacon of hope, was the Wizard Tower. Wreathed in its shimmering Magykal haze, it sent out a defiant blaze of indigo and purple. Nicko and Rupert exchanged strained smiles - all was not yet lost.

As they drew near to the New Quay they saw the welcoming lights of Sally Mullin's Tea and Ale House glowing in the gathering twilight and Nicko knew that he was right about the Darke Domaine. Sally Mullin's was safe. As they got closer, they saw through the steamed-up windows of the long, low wooden building that the place was packed with those lucky enough to have escaped and their spirits lifted - they were no longer the only ones.

But as the Port barge drew alongside the New Quay, a fearsome roar from the Castle - louder than they had ever heard before - sent the hairs on the backs of their necks prickling. Once more Rupert and Nicko exchanged glances, but this time without a trace of a smile. There was no need for words; they both knew what the other was thinking - how could anyone survive inside that?