“No hinges,” Lindy agreed. “No keyhole. Not the tiniest crack. It’s like it has no lid.”

“The little replica has a lid,” Nate said. “I can feel the lid.”

“Right,” Chris agreed. “Me too. It seems obvious on the guidestone.”

Nate tried to open the replica. The lid wouldn’t budge. “It’s locked.”

“Mr. White didn’t think we could open it underwater,” Chris reminded him. “We can give it a better try when we get it out of here. Should we see if we can move it?”

“Lindy?” Nate said. “Would you hold the replica?”

“Sure,” she said, accepting the transformed guidestone.

Chris went to one side of the chest, Nate to the other.

“Moving the chest could set off a trap,” Nate said.

“True,” Chris acknowledged. “Everybody get ready for trouble.”

“Go for it?” Nate asked.

“Why not?”

They lifted together. Nate found the chest a bit lighter than he expected. It had a fair amount of weight to it and was pretty bulky, but overall it felt manageable. Nothing indicated that lifting it had triggered any sort of trap.

“How is it?” Risa asked.

“Could be worse,” Chris said. “Let’s get out of here.”

Advancing through the water, Nate and Chris carried the trunk back to the tower and started gliding up the stairs. Risa and Lindy followed.

Taking the chest up the tall tower didn’t particularly fatigue Nate. Once they got some momentum going, the effort almost felt more mental than physical. They just kept toting the chest upward, keeping away from the stairs, walls, and ceiling.

At last they emerged from the lighthouse and brought the chest up to the surface of the bay. The air felt empty and dark after the vivid sensations available underwater.

Lindy and Risa surfaced nearby.

“So far, so good,” Lindy said.

“Should we try to fly with it?” Chris asked.

“Sure,” Nate said.

With the chest between them, Nate and Chris ascended out of the water. They hadn’t risen more than ten feet before Nate’s arms were trembling with exertion. The boys stopped rising, and Chris’s side of the chest dipped. Nate lost his grip, as did Chris, and the chest splashed down into the water.

Nate dove down and stopped the chest from sinking clear to the bottom. Chris took hold of the other side. The girls gathered near.

“It’s too heavy to go far,” Nate said.

“It isn’t bad underwater,” Chris noted. “We could take it through the water to Angel Island. Then we would just have to fly it a little ways to a quiet spot.”

“Alcatraz is closer,” Lindy said, “but Jonas nixed that as a destination, along with Treasure Island and Yerba Buena.”

“He left Angel Island as fair game,” Chris said. “The Tanks will have a tough time getting there. Let’s go see if we can open this thing.”

Chapter Eighteen

The Chest

Working together, with one of them at each corner, Nate, Chris, Lindy, and Risa managed to fly the chest a few hundred yards inland from the Angel Island shore, crossing a small road and struggling some distance up a brushy slope. When they reached their limit and let the chest thump down, it struck the ground with finality.

Risa rubbed her hands briskly. “I lost circulation to my fingers.”

“That thing was heavy,” Chris said, stretching his arms. “This spot seems as remote as anywhere.”

Nate ran a hand over the top of the chest, then down the side. Unlike his body, the chest remained damp. “I still can’t feel how to open it. I can’t even tell whether it’s wood or ceramic or what.”

“I can sort of see it with the moonlight,” Chris said. “The color is darker than I realized. But I had a much better sense of it back in the water.”

“Let me get out the guidestone,” Lindy offered. She had stashed it in her backpack so she could help carry the chest. “Maybe it has a key inside.”

“The chest has no keyhole,” Risa pointed out.

“Well, maybe there’s something else in it,” Lindy said, rummaging. “It seems suspicious that the guidestone turned into a miniature chest. At least the little replica has a lid.”

Lindy produced the tiny chest and started prying at it with her fingers. “It’s stuck, but the lid has some wiggle to it. Wait, here we go.” She lifted the small lid, and simultaneously the top of the chest folded open as well. And then the chest kept unfolding in astonishing ways, as if lid after lid were opening in unpredictable directions. With a startled squeal, Lindy dropped the miniature chest as it transformed as well, mimicking the larger version.

“Whoa,” Nate breathed, taking involuntary steps back as the chest grew and evolved with each new lid that lifted. The unfolding process sped up. Strange new shapes unfolded manically, expanding the chest to improbable proportions.

When the process ended, Nate found himself staring at the entrance to a stone building that extended back into the slope. The structure stood three times his height, with a triangular pediment supported by pillars. Because of how the building protruded from the slope, it looked as if it had been mostly buried in a landslide. A massive bronze door shielded the entrance.

“That was awesome,” Chris said.

“More like freaky,” Risa replied.

“I can’t see inside,” Lindy said. “Same as with the chest.”

Nate crouched, pointing at the ground. “Look, the guidestone matches the chest’s new shape. It’s even partly buried.”

“What’s with the guidestone?” Chris asked.

“It must be some sort of simulacrum,” Nate said. “I think touching it to the chest activated it.”

“Opening the guidestone chest made the actual chest transform,” Lindy said.

“So what happens if we open the little door?” Risa worried. “Will it change again? Will it turn it into a spaceship?”

“Let’s try the actual door first,” Chris suggested. He walked to the entrance of the building and tugged on the bronze door. It didn’t budge. Planting himself firmly, he pulled hard but still got no result.

“It might take them some time, but the Tanks are coming,” Nate said. “We should probably try the little door.”

Lindy crouched and opened the door of the small building. The door to the large building opened in perfect synchronization. Nate was braced for something more, but nothing else happened.