What are we waiting for?” said Castor.

He climbed onto Nera’s back, settling himself amid her gold fur. Now that they were no longer fighting, Tanner could see that Castor’s Beast had intricate markings in her fur. Her face was patterned with darker streaks, and patches of gold and chestnut rippled across her body. Nera batted at Castor playfully with her paw, claws gleaming as she pushed him up her side so that he was able to scramble onto her neck. He pressed his hand to the top of her head, and the Beast seemed to calm down.

“What will you do when you find your brother again?” he asked.

Gwen climbed onto Gulkien. The wolf shook himself and snapped at the air, as if he was stretching his jaws. “I don’t know,” she said quietly, staring straight ahead and refusing to look at either of them.

“We’ve all lost something or someone,” said Tanner. “But Derthsin’s going to pay.”

As they were about to take off, Gwen cried, “Wait! Castor, won’t you be missed here? Isn’t there anyone you need to say good-bye to?”

Tanner saw him tense. “No. No one.”

Gulkien and Firepos beat their wings and soared into the air, their shadows rippling over the village square. Firepos’s feathers shone like bronze as they ruffled in the breeze, and Gulkien’s fur flattened over his long snout. Nera raced ahead, across the land, leaping from hillock to valley, her tail flying out behind her. Tanner had never seen a Beast move so fast across land.

Castor and Nera led the way. From up above, the two other Beasts banked around until they were heading toward the Northern Mountains where the Hidden Mines must be. Low, ugly gray clouds hung over the mountainside. Ahead, the ground was dark.

They passed through chilly clouds, toward the steep, iron gray faces of the Northern Mountains. The two winged Beasts flew single file up a pass threaded with a silver stream, and the vegetation petered out below. Nera leaped from rock to rock, her claws sending out sparks. Nothing seemed to slow her down, not even the barren land and thin air.

Sharp-edged shadows were cast by the mountain rocks and jagged peaks. Boulders and crumbling drifts of black-slate rock wound like dry rivers up the mountains. Castor whistled, and Nera raced up a riverbed, only to loop back — all in the time it had taken Gulkien and Firepos to fly the same distance. Castor called up: “I bet your Beasts can’t fly that fast!”

“Of course they can,” Tanner said, not wanting to admit the truth. Nera was faster.

Nera shot back and forth in maddening bursts. Firepos’s feathers shook in the air with her steady wing beats, and Gulkien’s wings creaked and stretched on the wind gusts. Nera was toying with them.

“Prove it,” Castor yelled. “Let’s see if you can keep up!”

“You’re on!” Tanner called down. “Oh, and Castor? If I beat you to the next mountain, you have to be quiet for the rest of the trip.”

Castor smiled and sat back, his hands behind his head, so he was holding on to Nera with only his thighs. “And if I beat you,” Castor said, “you have to give me your sword.”

“I’m not going to give you my sword, Castor.”

“Just until we get there,” Castor shouted. “Besides, I thought you said your bird was fast.”

Tanner glanced at Gwen. “All right, Castor. Ready …”

Castor said, “Set …”

They hunched forward.

“Go!” Gwen yelled.

Tanner and Castor stared in astonishment as Gulkien streaked ahead of them, his paws tucked up underneath him, his leathery wings flapping hard.

“Now, Firepos!” Tanner shouted.

Castor yelled, “Go, Nera!”

The boys and their Beasts raced after her. Tanner held tightly to Firepos’s neck, his eyes streaming in the rushing air. She shot like an arrow after Gulkien, her wings close to her back. Below Firepos, Nera ran in a rapid, frantic rhythm. Her huge paws thudded against the rocks and her coat rippled as she darted from boulder to mountain ledge. Gulkien’s movements in the air were more measured and even, while Firepos used her wings only occasionally, zooming as straight as a dagger through the sky. Tanner could hear Castor shouting encouragement to Nera below them.

As they burst over the pass at the end of the valley, Gulkien suddenly pulled back, directly into the path of Firepos’s flight. Nera jerked to a stop below them, and Firepos beat her wings to stay in the same spot of mountain air.

Castor shouted, “What’s the matter with you two? We’re still racing!”

“No, we’re not,” Gwen said.

“Why?” Castor demanded.

“Look.”

A black mountain range of three peaks loomed ahead of them. Plumes of gray-white smoke rose amid the summits. The mountains tapered into ugly spikes that seemed to stab at the sky, and as they flew closer, Tanner realized the smoke was coming from long slits in the high rock. Vents, he thought. The kind an armory would need.

They flew between the peaks. Just as Castor had said, the inner slopes fell into a deep cavity, the bottom of which was filled with gray water. About halfway up the nearest black mountain, Tanner spotted a square entrance, braced with wooden supports, like a mine shaft.

“Why aren’t there guards outside?” Gwen called over the wind.

“Maybe Derthsin doesn’t think he needs them,” Tanner said. “Remember how his soldiers were attacking ordinary farmers, just because they could? Derthsin is overconfident.”

Castor urged Nera on. “Beat you there!”

“Castor, wait!” Tanner shouted. The time for games was over. Firepos dove after them in a steep drop that made Tanner’s stomach jump. He gripped Firepos’s feathers — the ground was rushing up too fast. Firepos pulled out of her dive and glided to land at the cave entrance. Nera arrived beside her, and a moment later, Gulkien brought Gwen down. After they all dismounted from their Beasts, Gulkien began to stalk the area outside the cave, sniffing and growling. Firepos sat seriously, her head poised to watch the sky. Nera paced and scratched the rock impatiently, her gold fur rippling.

“Impressive,” Castor said. “At least your bird knows how to dive.”

“That’s enough!” Tanner snapped at him. He raised a finger to his lips. “This place is dangerous. We need to be quiet.”

Tanner felt the ground trembling. Pebbles danced and shook, and as he approached the cave, he heard a heavy metallic clanking and banging. There was a distant hiss, like steam being released, and then the noise of metal striking metal sounded even louder. A low voice boomed over the racket, barking unintelligible orders, bellowing from somewhere deep inside the earth. Tanner hesitated at the dark cave entrance. It sounded like the noise of dungeons and nightmares. He heard Castor and Gwen approach behind him.

“I’ll see what’s happening,” Tanner whispered. “I’ll go as far as I can without being seen.”

“We should all go,” Gwen said. “Geffen might be in there.”

“No, it’s too risky,” he said. “Only one of us needs to see what’s happening to come up with a plan.”

To Tanner’s surprise, Castor didn’t put up a fight. Instead, he stayed on Nera’s back. His face was dark and unreadable. His mood has changed, Tanner thought.

“All right. We’ll wait with the Beasts,” Gwen said. “Be careful.”

Firepos squawked and shuffled closer. Tanner forced a smile. “Don’t worry. I’ll be back before you know it.”