Without thinking, he sat and tugged his sneakers off. "Who's going with me?"

"Wade, you're not going down there," Becca snapped.

"Yes, I am. This is the cave! You know it is. Shoichi knew it. Laura Thompson knew it. They all knew it. Vela is down there. I'm going in-"

Becca clutched his wrist tight. "You are not."

"Look, the Order will find Vela if we don't. Or kill us all. Or both. Either way, we have nothing to deal with if they find it first. I'm going down there!"

Becca tore off her sneakers and tossed them next to his. "Not alone, you're not."

Lily stared at Darrell. "Oh, I have a bad feeling about this. What if there's no outlet? You guys could drown trying to find your way back. This is super nuts."

"If there's no way out, then we'll come back up. Simple," said Becca.

So. She's thinking, too, Wade thought. At least one of us is!

"Keep watch," he said. Which he realized was dumb, but he couldn't think of anything else to say. He climbed down over the ledge to the rocks as far as he could, then dropped straight into the pool. The water was colder than he expected. He felt Becca splash next to him. He surfaced. She surfaced.

"Fresh water," he said. "Rainwater. You're right, Darrell."

"Omigod, if you don't come back, I'll kill you!" said Lily.

Wade gulped in a mouthful of air, plunged his head down, rolled over in the water, kicked his feet, and swam downward toward the source of the light. As he hoped, the passage opened into a brighter space. Turning his head to the dark water behind him, he couldn't see anything, felt only the cold. He hoped Becca was there, but he didn't know how long his lungs would hold out. He had to keep swimming forward. The passage was longer than he thought it would be. Deeper. The light dimmed suddenly. Had he taken a wrong turn? There was no opening. He kept swimming. Then his lungs began to tighten and burn. They screamed to take in air.

He pushed forward, swatting the water behind him, no breath left. Except now he wasn't sure he actually was going forward. It was like being in a coffin. His arms seemed like lead pipes. His lungs felt as if they were turning to water. Where did the light go? In his mind he screamed, Becca, go back! We're trapped. I'll go on, but you go back! Save yourself! Save- The passage angled up. There was the light again.

With one final push of his leaden arms, he burst up inside a cavern that seemed as bright as the sun. Becca splashed up beside him, desperate for breath. They hung there in the water, their fingers clutching the rocks, gasping and coughing for minutes. They finally crawled up and flattened themselves on a stone floor, staring upward.

When he spied a small opening at the faraway top, Wade surprised himself by starting to laugh. The cavern's light was actually dim, but it seemed brilliant. They could feel raindrops falling in the opening, through the vault, and down over them, sprinkling their faces. It was as quiet in there as if they had surfaced on another planet, and he laughed and couldn't stop laughing.

"Wade . . ."

Becca pointed at the walls. They were carved and painted with hundreds of symbols. Stars. Constellations. A blue hand was printed on the wall in the midst of the stars, its fingers pointing down.

Becca slapped his arm gently. "We found it."

Chapter Fifty-Three.

Wade stood, still breathing hard, his legs like rubber, boneless.

The cave walls formed an irregular cone of rock that had kind of the feeling of an ancient cathedral or temple, a holy place of stone.

The perfect place to hide a priceless artifact.

"If Shoichi knew this cave, he may have watched the stars through the hole in the ceiling," he said. "Maybe he added some of these drawings himself."

"Except . . ." Becca was up now, searching the walls, the floor, the high vault, everywhere for a sign. "I don't see a blue stone." She glanced back at the pool. "Could it be . . . hidden underwater? Did we pass it on our way here? I mean, maybe over the years since Magellan the passages filled up with water. Or maybe the cave collapsed, changed its shape."

Wade stepped over to the blue handprint. "But Laura Thompson must have seen the relic, right? Janet told us about her last trip here. That wasn't that long ago."

"I forgot that." She scanned the walls up and down. "Then I have no clue."

No clue. Except maybe there was a clue.

Studying the upside-down handprint, Wade realized that it not only vaguely bore the shape of a sea star, but that the palm and fingers formed a distinct geometric shape. "Bec, what does it remind you of?

She stood back. "An upside-down hand?"

Wade laughed again. "And . . ." He traced his finger in straight lines around the angles the hand made. "It's kind of a triangle, isn't it? With the wrist as the top point. The same triangle as in Pigafetta's drawing. The same shape as the lateen sail. All pointing to a location. Up the cave wall."

They followed the point of the imaginary triangle up the wall. About ten feet from the floor was a narrow horizontal shelf of rock, an outcropping of volcanic limestone.

Becca looked at Wade. "You don't think . . ."

"I'll give you a boost."

"You'll . . ."

"Come on." Wade wove his fingers together, and she stepped in with her left foot, holding on to his shoulders. Wade lifted, and she set her right foot on his shoulder, then her left, bracing her hands against the cave wall. She steadied herself, reached up, and felt over the ledge.

"Anything?" he said.

Becca stiffened.

"What is it? What do you see?"

She drew her arm slowly away from the wall, gripping something in her hand. She made a choking sound. "Oh, Wade."

When he saw the wavy blade of the dagger, his knees nearly buckled. "Magellan's dagger! The one Copernicus gave to him with Vela! Is there anything else?"

Quickly slipping the dagger into her belt, she reached up again. "The dagger was stuck partway into the cave wall. Taking it out revealed an opening, a kind of compartment." Wade held her calves as she raised herself up on her tiptoes. One foot left his shoulder. Then her arm swung back and she lurched away from the wall. He twisted, catching her clumsily, and they fell to the floor together.

"Wade-" Becca opened her hand.

In her palm was a nearly perfect triangle of dazzlingly blue stone.

Roughly four inches long on two sides and two inches at the base, it was a smooth piece of lapis lazuli with a slight curve in one side. It was in a shape very similar to a lateen sail.

"Argo Navis Vela," Wade said in a whisper.

It instantly seemed as if all the air in the cavern, and all the light in the air, drew itself into the stone.

Vela pulsed with a kind of life, he thought, though he knew it wasn't possible. It seemed to him as if time and space combined and-he didn't even know what else-people, maybe, or family, or blood, or love, or something-were all joined inside the contours of the blue stone.

And it breathed.

It breathed and whispered secret after secret, but only to the two of them who were there.

This was before he even held the stone! Vela was luminescent, beautiful, and alive, and then Becca slipped it into his trembling hand, and he felt what he thought was the weight of history in his palm, as if the stone weighed a thousand pounds or was as weightless as light.

"Becca . . . ," he murmured, tearing his eyes away from it to look into hers for only seconds before the stone drew him back to it. He slumped on the floor of the cave, his brain clicking away with a kind of clarity he was certain he'd never known before.

"Becca . . . ," he said again, discovering something amazing, yet painful, about the stark syllables of her name. "More than all the craziness, the running, and the places and the arrows and the hiding and everything, through all the stuff we read and the sketches and equations and everything we found out, this blue stone proves there's a time machine. It's not like a math proof, but I . . ."

As he trailed off, Becca wiped a tear from her cheek, nodding.

"I guess what I'm saying is that holding it in my hand makes Copernicus's astrolabe as real as if it's right here, and we're traveling back in time right now, you know?"

"I know."

"And no matter how impossible it is to do that, this is a part of a time machine, a relic of Copernicus's astrolabe, the astrolabe that could travel in time, the thing was a time machine, that actually existed, and this is a relic of it and we're holding it and it's real . . ."

Becca smiled. "You realize that's kind of a wormhole of a sentence."

"Yeah, I guess it is." Wade started laughing again, and the echo of his laughter coiled up the sides of the stone room, coming back down from the top and going back up again.

He didn't know how many minutes passed while they simply stared at the stone as if they were waiting for something to happen. It was like time itself had stopped, which is a thing only time machines can do.

Becca took it gently from his palm and turned the stone over.

On its back were a faint but perfectly engraved spiral and two small notches at the base of it that held minute traces of something dusty and red.

"Rust," Becca said. "Where the stone was in contact with metal."

Wade wanted to laugh again. He knew instantly where the rust marks had come from and began to feel the sketch of the device come whirring to life right there. "That's where Vela was attached to, what did he call it, the 'grand armature' of the astrolabe. Becca-"

The water bubbled suddenly, the silence broke, and Darrell and Lily splashed into the cave. "They're here! They're right behind us-"

The pool exploded. Four divers climbed out and stood on solid ground. Two men armed with underwater pistols. A pale man who lifted his scuba mask and dried his spectacles.

And the beautiful young woman with the wickedly ugly crossbow.

The Knights of the Teutonic Order.

Chapter Fifty-Four.

The young woman was impossibly beautiful. Otherworldly, Wade thought. Like a cross between a supermodel and a futuristic automaton. And her hair. Even dripping wet it was awesome.

He glanced over at Lily, Darrell, and Becca. They had to feel it, too. The woman wasn't much older than they were, but she had some kind of crazy kinetic energy running through her.

And that crossbow she held. What was that thing? An artifact from some ancient future? A weird robotic extension of her arms?

"You have witnessed the reach of the Teutonic Order," she said with a trace of accent he couldn't identify. It was almost hypnotic how her voice echoed up the walls of the cave. "You know our power. Let it not be the last thing you know. Give me the relic."

She took a step toward him, as did the three men, but Wade raised his hand. "I'll smash it!" he cried. "I will!"

She stopped. Everyone stopped.

Dangling around her neck, just visible in the opening of her form-fitting outfit, were two ruby stones, an identical pair of sea serpents with several arms. Krakens.

The hunched man beside her adjusted his thick-lensed spectacles. His suit was baggy in the chest, stretched in other places. He looked other than human in the opposite way. A misshapen little gnome.

"Since Berlin, you have taken us on quite a journey," the man said weakly. "It ends here. In this forsaken cave." His voice was halting, his words overenunciated.

"You killed Heinrich Vogel," Becca said, shifting to stand next to Wade. "And Bernard Dufort in Paris."

"Among others," said Galina, her eyes staring not at her but at Wade's hand, as if to burn it away and free the relic for herself.

"Countless others," the gnome added proudly.

"You're all horrible creeps," Lily said softly. Her eyes were pinched and fiery. "Every one of you."

"Why don't you give me the relic," Galina Krause said. It was not a question. Removing her left hand from the shaft of the crossbow, she held it out. The barrel barely moved. The weapon must either be lightweight, Wade thought, or she's very strong. It was still pointing steadily at his heart.

"The old man is your father?" she said. "Thanks to the Guardians, he escaped our grasp in Berlin. He will not come for you now. You are alone."

Wade felt his breath die. Had they shot him? "You . . ." was all he could say.

"He'd better not be hurt," said Darrell, shifting from one foot to the other, ready to spring into action.

Wade pulled himself from the thought of his father hurt. He tapped Darrell's left foot with his own, and he stopped moving.

Wait, Darrell, wait for it . . .

"Save yourselves a lonely death," the gnome said, stepping forward once more. "Give us-"

Wade backed up. "Not an inch!"

The thousand thoughts flashing through his mind balled up into a single one. Passing through that underwater tunnel, he and his friends had become different people.

How else to explain his own behavior with these killers, holding the relic high, ready to shatter it to dust on the cave floor?

The water had changed them. The light in the cave had changed them. The relic-the blue stone in his palm right then-had changed them, was changing them that very moment.

We've become Guardians, he thought. That's what it is. We're members of the secret society from Copernicus to Magellan to Enrique and Pigafetta and Shiochi and Laura Thompson and her granddaughter and all the countless others, on and on, through the centuries, with one goal-to protect the Copernicus Legacy.