Septimus had noticed too. The smooth run had changed to an unpleasant shake that came up from the runners and was giving a bone-jarring ride. The low background rumble had become so loud that Septimus had to raise his voice to be heard.

“Perhaps we had better slow down,” he said. “If something is wrong and we crash at this speed . . .”

“I’m going to put the brake on,” said Jenna, moving her left foot across to the broad plate that came up from the floor on her side.

“Yep. Good idea.”

Cautiously, Jenna pressed her foot down on the brake. The Tube slowed to a crawl, but the shaking became even more pronounced.

“Something’s wrong!” said Jenna, snatching her foot off the brake.

Suddenly, Septimus realized what it was. “It’s the jinn, Jen!”

“Oh, do stop saying silly rhymes, Sep. This is not nice. Oh!” The Tube gave a particularly big lurch and Jenna fell sideways.

Septimus caught her. “It’s okay, Jen. I know where we are. And I know what’s happened. It’s the ice. It’s really churned up—look, you can see it in the headlight. This must be where the warrior jinn marched to the Castle, which means that we must be under the Isles of Syren now.”

Jenna peered through the glass. “Hey—you’re right!”

“No need to sound so surprised,” said Septimus, grinning.

Jenna thought about what Septimus had said. “So we are under the sea now, right?”

“Yes. I suppose we are.”

Jenna shivered. “All that water above us, Sep. It’s so . . . scary.”

Septimus didn’t want to think about it. “I’ll speed up and get us out of here.”

“Not too fast, okay?”

Septimus pressed the pedal on his side of the floor; the Tube picked up speed and settled into a gentle bumping along the rutted ice.

After some minutes Jenna said, “Is there an Ice Tunnel hatch below the Palace, Sep?”

“I suppose there must be. I’ve never seen it though.”

Jenna sighed. “I wish Beetle were here. He’d know.” She turned to Septimus. “Everything feels kind of right when Beetle’s around, don’t you think?”

“Perhaps you ought to tell him that sometime,” said Septimus, giving Jenna what Sarah Heap would have called a meaningful look.

Jenna went pink. “Shut up, Sep,” she said.

“Okeydokey. Now I’ve been thinking. There’s a sign to the Wizard Tower in the Ice Tunnel below, so I bet there’s a sign to the Palace too.”

“So how near do you think we are?” Jenna asked.

“We can’t be too far,” said Septimus. “It didn’t take very long from the House of Foryx to the Isles of Syren, did it? And the Castle is much closer.”

“Perhaps we ought to slow down,” said Jenna anxiously. “We don’t want to miss the sign and get lost under the Castle.” The Tube hit a particularly deep rut and shook alarmingly. “Slowly, Sep!”

“Don’t panic, Jen.”

“I am not panicking. You are going way too fast.”

Irritated, Septimus slowed the Tube to an uncomfortable bump while Jenna stared out of the thick green glass screen, searching for a sign to the Palace.

After some minutes, Jenna said, “How big did Hotep-Ra say this pyramid was? I mean, is it like head-size or more kind of nose-size?”

“Nose-size,” said Septimus. “He said it would sit comfortably on your hand.”

“That’s really small,” said Jenna gloomily.

“And the Palace is really big,” Septimus said equally gloomily.

“The only thing I can hope for is that my mother, the Queen, will tell me where it is.”

Septimus looked at Jenna. “Do you think she will?”

“No,” said Jenna. “Sep, look out!”

Septimus snatched his foot off the power pedal. “Jen—brake, brake, brake!”

In the bright beam of light of the Tube, Jenna and Septimus saw the most bizarre sight. Poking up from the floor of the Ice Tunnel were the head and shoulders of a man. He was staring at the oncoming Tube in utter horror. Jenna slammed her foot on the brake and the Purple Tube skidded to a halt just in time. The head-and-shoulders stayed where it was and continued to stare, its mouth opening and closing like a goldfish thrown out of its bowl.

“Jeez. It’s Marcellus.” Septimus reached over to the hatch dial and clicked it up, the pilot hatch swung open and in seconds he was up and out into the chill of the Ice Tunnel, clambering down the ladder and running and sliding across the ice toward Marcellus, closely followed by Jenna.