Nicko untied the dinghy from the Royal Barge, and under the cover of the giant cedar trees, they slipped away from the Palace landing stage. It was a tight squeeze in the small boat. The NightUllr stood at the prow, his green eyes shining in the dark with Snorri squashed in beside him. In the middle sat Nicko, steadily rowing them upstream, away from the Palace. Jenna and Septimus huddled together in the stern, shivering in the chill that rose from the water, brushing off the fat, lazy snowflakes that were drifting down from the sky. They were all wrapped up in an assortment of UnderCooks' coats, but the cold air easily found its way through the cheap thin wool - for Palace UnderCooks did not get paid enough to buy decent outerwear.

They were on their way to the Great Chamber of Alchemie and Physik. Septimus knew it was their only chance to return to their own Time and he didn't hold out much hope. He was not in a good mood. "This is not going to be easy," he told them. "Only Marcellus has the Keye to the Great Doors of Time."

"Well, we will just have to lie in wait in the Chamber and ambush him when he comes in," said Nicko breezily. "It's four against one, not bad odds."

"You've forgotten the seven scribes," said Septimus.

"No, you've forgotten those, Sep. You didn't say anything about seven scribes. Oh, well, four against eight then." Nicko sighed. "Anyway, we've got no choice. Otherwise we're stuck here forever."

"Do not forget Ullr," murmured Snorri, "if we arrive before daybreak."

Nicko upped his pace. He'd rather have a panther on his side than a scraggly orange cat any day. Jenna turned back to look at the Palace, which was rapidly disappearing behind them. The fruitless search of the Palace had been completed, and each room now had a candle burning in it; the long, low yellow stone building was ablaze with light, its wide lawns spread out before it with their fresh snowfall like a crisp white cook's apron. Despite knowing that Queen Etheldredda was somewhere within those walls, Jenna could not help but think that it was a wonderful sight to see the Palace so alive, and she decided that if, by some miracle, she ever returned to her Time, she too would light up every room - in celebration.

Jenna looked up at the windows of Esmeralda's - and her - room. "I am glad Esmeralda got away," she said.

"So am I," said Septimus.

Jenna was amazed. "You knew Esmeralda?" she asked.

Septimus nodded. "She only just made it, you know. Marcellus took her through the Queen's way, but they nearly got caught by the Steward. Then - and this is the good part - he threw her cloak into the water just above the Palace on an outgoing tide and made sure one of the footmen fished it out. Everyone thought she had drowned, and Etheldredda was thrilled, seeing as, according to Marcellus, she had been planning to throw Esmerelda into the bottomless whirlpool in Bleak Creek."

"Marcellus took her?" asked Jenna.

"Well, he is her brother. Esmeralda came to stay with him and she was really nice to me. No one else spoke to me then because they were jealous that I was the Apprentice and they were still just scribes."

Jenna remembered the diary. "So the new Apprentice ... was you?"

Septimus nodded. He lifted up his servant's tunic and showed Jenna his black, red, and gold Alchemic robes underneath. "See? Alchemic Apprentice stuff."

With another pull on the oars, Nicko took them around the next bend, and the Palace was lost from view. They were now approaching a long-forgotten dockyard on the east side of the Castle. The river was deeper here than Nicko was used to in his own Time, the wind was picking up and the current was fast and strong. The little rowboat shot quickly past dozens of tall ships that were moored up for the winter along the shore. The ghostly hum of the wind in the ships' rigging sent even more shivers down the spines of the occupants of the Queen's dinghy, and the long beards of frost that had settled on the complicated traceries of rope and now shone in the moonlight like great silvery cobwebs did nothing to make them feel any warmer.

"Is it much farther, Sep?" Nicko inquired, his breath coming in rapid bursts of warm cloud on the frosty air. He brushed away the snowflakes settling on his eyelashes.

"It can't be far," said Septimus, peering at the piles of rubble and great towers of scaffolding that were springing up from the riverbank.

"If you've never been down this underground river, how do you know where it is?" asked Jenna, her teeth chattering.

"The Underflow comes out at the Alchemie Arch, Jen. There's a map on the wall showing where it goes. I've spent hours with nothing to do but stare at that map. And there's a gold Alchemie sign above the arch. A circle with a dot in the middle that's meant to be the Earth going around the sun. Then there are seven stars around that. Alchemists like sevens - worse luck." Septimus sighed heavily.

"Oh, do cheer up, Sep," said Jenna. "At least we're all in this together now."

As Nicko rowed, everyone stared at the wall that rose up from the river, hoping for a sight of the Alchemie sign. But all they could see was stones, scaffolding and half-finished walls that reared up into the cloudy night sky. One by one, Jenna, Nicko and Septimus realized what they were looking at.

"They're building The Ramblings,"Jenna said very quietly.

"I know," said Nicko. "It's weird."

"We haven't even been born yet," said Jenna.

"Or Mum, or Dad. It makes my head go funny."

Septimus sighed. "Don't even think about it, Nik. It makes you feel like you're going crazy."

Snorri took no part in the conversation. The Ramblings meant nothing to her and the Castle was as strange to her in this Time as it had been in her own Time. Also Snorri had grown up in a land where many people knew that Time could be long or short, go backward or forward, where Spirits came and went and where all things were possible. She sat quietly and scanned the walls for the Alchemic sign.

"Shh," Nicko suddenly whispered. "There's a boat behind us." Jenna and Septimus turned to look. It was true. If they listened hard, they could hear the splash of the oars of a small rowboat. A voice reached them across the water.

"Faster, men. A shilling and a fine cloak to you all if we catch them. Faster."

"Nicko," whispered Jenna. "Nicko - hurry!"

But Nicko was getting tired. He tried to speed up his pace but found he could row no faster. Jenna and Septimus could do nothing but watch their pursuers draw ever closer until they could clearly see four large shapes precariously perched in a long, narrow rowboat, which was gaining on them quickly.

Snorri paid no attention to the pursuers, but kept her eyes on the wall below the beginnings of The Ramblings. All of a sudden, she said, "I think that the sign that you look for is there."

"Where?" asked Nicko.

"It is there, Nicko," Snorri replied, enjoying saying Nicko's name. "See, it is above the dark archway where the stream runs out into the river. Below the wall with two windows."

"Okay," said Nicko. He did a quick turn and, finding a little extra energy, rowed at top speed into the dark archway, where he stopped to catch his breath. The sound of the approaching rowboat drew nearer, but Nicko dared not pick up his oars for fear of making a telltale noise. Everyone held their breath, watching the small gap in the darkness that showed the empty moonlit river. At lightning speed, their pursuers went past so fast that if anyone had blinked just then, they would have missed it.

"They've gone," breathed Jenna, sinking back into the boat with relief. Nicko picked up the oars reluctantly. He realized that he was going to have to row the boat underground, and was none too happy at the thought. Trying to ignore the beginnings of a panic welling up inside him, he started to row deeper into the darkness.

"That plaque was like the one above the Dragon House, only not so worn away," said Jenna.

"Anything under the Castle or in the walls is old Alchemie stuff, Jen," Septimus said, his face eerily illuminated from below by the light from his Dragon Ring.

"Even the Dragon House?" asked Jenna.

"Especially the Dragon House."

Jenna looked at Septimus. He did not return her glance but stared straight into the dark. He seemed distant, weighed down and much, much older than his extra one hundred and sixty-nine days. For a moment Jenna felt afraid of what Septimus had become while he had been away. "You know a lot of things now, don't you, Sep?" she said rather than asked.

Septimus sighed. "Yeah," he said.

Nicko hated the UnderFlow. The stream smelled odd for a start: kind of musty and rancid as though something had recently died in it, and there were things - soft, squishy things - floating in the water; he could feel the ends of his oars touching them. The tunnel was just not quite wide enough for the stretch of his oars, so with every stroke, the edge of the blades scraped along the side of the wall and a few times brought the boat to a halt. Nicko was forced to pull the oars farther into the boat and row in an awkward rhythm so that the ends did not hit each other.

Nicko could deal with the irritations of rowing, but what he could not stand was the feeling of going ever deeper underground. With every stroke he took, Nicko felt the panic rise higher in his throat. Icy water dripped from the roof of the arched tunnel, which he knew was no more than an arm's length above his head. The whole tunnel was lit only by the dull yellow glow from Septimus's Dragon Ring, and with every pull on the oars, Nicko imagined the walls closing in on him. It was only the presence of Snorri sitting behind him that stopped him from dropping the oars and yelling "Get me out of here." Nicko closed his eyes and tried to imagine he was rowing in the wide-open ocean, for it made no difference whether he could see where he was going or not. There was only one way to go.

About twenty minutes later, which to Nicko had felt more like twenty hours, he knew that even the thought of the ocean and of Snorri sitting behind him could no longer keep his panic at bay. Fortunately Septimus said, "Here we are, Nik, we're in the UnderFlow Pool. You can open your eyes now."

"They were open," said Nicko indignantly. He opened his eyes and saw that they had come to a pool in a huge circular cavern. There was a long stone quay along one side, which was lit by a line of rushlights placed in holders on the walls. The water was inky black with flashes of orange reflecting the flames, and Nicko, who had an instinct for the depth of water, knew that it was very, very deep. But it was not the water Nicko stared at - it was the beautiful lapis lazuli arched roof that spanned the pool.

"The Dragon House," said Jenna, "it's the same as the Dragon House."

"Shh," whispered Septimus. "Someone might hear us, sound carries here." Quietly, Nicko rowed to the quay and held the dinghy steady. Ullr took a flying leap and landed with a soft thud on the smooth stone. He was followed by Snorri, then Jenna and Septimus. Nicko got out and went to tie the boat to a nearby bollard but Septimus stopped him. "No, shove the boat back into the tunnel where no one can see it, Nik, and let's get going."

Very reluctantly, Nicko gave the dinghy a push into the tunnel and watched it float away. "We're burning our boats, Sep," he said. "I hope you know what you're doing."