“I thought the owl was Minerva’s symbol,” Jason murmured.

“The screech owl is one of Hades’s sacred animals,” Nico said. “Its cry is a bad omen.”

“This way.” Hazel pointed to a doorway that looked the same as all the others. “It’s the only one that won’t collapse on us.”

“Good choice, then,” Leo said.

Frank began to feel like he was leaving the world of the living. His skin tingled, and he wondered if it was a side effect of the poison. The pouch with his firewood seemed heavier on his belt. In the eerie glow of their magic weapons, his friends looked like flickering ghosts.

Cold air brushed against his face. In his mind, Ares and Mars had gone silent, but Frank thought he heard other voices whispering in the side corridors, beckoning him to veer off course, to come closer and listen to them speak.

Finally they reached an archway carved in the shape of human skulls—or maybe they were human skulls embedded in the rock. In the purple light of Diocletian’s scepter, the hollow eye sockets seemed to blink.

Frank almost hit the ceiling when Hazel put a hand on his arm.

“This is the entrance to the second level,” she said. “I’d better take a look.”

Frank hadn’t even realized that he’d moved in front of the doorway.

“Uh, yeah…” He made way for her.

Hazel traced her fingers across the carved skulls. “No traps on the doorway, but…something is strange here. My underground sense is—is fuzzy, like someone is working against me, hiding what’s ahead of us.”

“The sorceress that Hecate warned you about?” Jason guessed. “The one Leo saw in his dream? What was her name?”

Hazel chewed her lip. “It would be safer not to say her name. But stay alert. One thing I’m sure of: From this point on, the dead are stronger than the living.”

Frank wasn’t sure how she knew that, but he believed her. The voices in the darkness seemed to whisper louder. He caught glimpses of movement in the shadows. From the way his friends’ eyes darted around, he guessed they were seeing things too.

“Where are the monsters?” he wondered aloud. “I thought Gaea had an army guarding the Doors.”

“Don’t know,” Jason said. His pale skin looked as green as the poison from the chalice. “At this point I’d almost prefer a straight-up fight.”

“Careful what you wish for, man.” Leo summoned a ball of fire to his hand, and for once Frank was glad to see the flames. “Personally, I’m hoping nobody’s home. We walk in, find Percy and Annabeth, destroy the Doors of Death, and walk out. Maybe stop at the gift shop.”

“Yeah,” Frank said. “That’ll happen.”

The tunnel shook. Rubble rained down from the ceiling.

Hazel grabbed Frank’s hand. “That was close,” she muttered. “These passageways won’t take much more.”

“The Doors of Death just opened again,” Nico said.

“It’s happening like every fifteen minutes,” Piper noted.

“Every twelve,” Nico corrected, though he didn’t explain how he knew. “We’d better hurry. Percy and Annabeth are close. They’re in danger. I can sense it.”

As they traveled deeper, the corridors widened. The ceilings rose to six meters high, decorated with elaborate paintings of owls in the branches of white poplars. The extra space should have made Frank feel better, but all he could think about was the tactical situation. The tunnels were big enough to accommodate large monsters, even giants. There were blind corners everywhere, perfect for ambushes. Their group could be flanked or surrounded easily. They would have no good options for retreat.

All of Frank’s instincts told him to get out of these tunnels. If no monsters were visible, that just meant they were hiding, waiting to spring a trap. Even though Frank knew that, there wasn’t much he could do about it. They had to find the Doors of Death.

Leo held his fire close to the walls. Frank saw Ancient Greek graffiti scratched into the stone. He couldn’t read Ancient Greek, but he guessed they were prayers or supplications to the dead, written by pilgrims thousands of years ago. The tunnel floor was littered with ceramic shards and silver coins.

“Offerings?” Piper guessed.

“Yes,” Nico said. “If you wanted your ancestors to appear, you had to make an offering.”

“Let’s not make an offering,” Jason suggested.

Nobody argued.

“The tunnel from here is unstable,” Hazel warned. “The floor might…well, just follow me. Step exactly where I step.”

She made her way forward. Frank walked right behind her—not because he felt particularly brave, but because he wanted to be close if Hazel needed his help. The voices of the war gods were arguing again in his ears. He could sense danger—very close now.

Fai Zhang.

He stopped cold. That voice…it wasn’t Ares or Mars. It seemed to come from right next to him, like someone whispering in his ear.

“Frank?” Jason whispered behind him. “Hazel, hold up a second. Frank, what’s wrong?”

“Nothing,” Frank murmured. “I just—”

Pylos, the voice said. I await you in Pylos.

Frank felt like the poison was bubbling back up his throat. He’d been scared plenty of times before. He’d even faced the god of Death.

But this voice terrified him in a different way. It resonated right down to his bones, as if it knew everything about him—his curse, his history, his future.

His grandmother had always been big on honoring the ancestors. It was a Chinese thing. You had to appease ghosts. You had to take them seriously.

Frank always thought his grandmother’s superstitions were silly. Now he changed his mind. He had no doubt…the voice that spoke to him was one of his ancestors.

“Frank, don’t move.” Hazel sounded alarmed.

He looked down and realized he’d been about to step out of line.

To survive, you must lead, the voice said. At the break, you must take charge.

“Lead where?” he asked aloud.

Then the voice was gone. Frank could feel its absence, as if the humidity had suddenly dropped.

“Uh, big guy?” Leo said. “Could you not freak out on us? Please and thank you.”

Frank’s friends were all looking at him with concern.

“I’m okay,” he managed. “Just…a voice.”

Nico nodded. “I did warn you. It’ll only get worse. We should—”

Hazel held up her hand for silence. “Wait here, everybody.”

Frank didn’t like it, but she forged ahead alone. He counted to twenty-three before she came back, her face drawn and pensive.

“Scary room ahead,” she warned. “Don’t panic.”

“Those two things don’t go together,” Leo murmured. But they followed Hazel into the cavern.

The place was like a circular cathedral, with a ceiling so high it was lost in the gloom. Dozens of other tunnels led off in different directions, each echoing with ghostly voices. The thing that made Frank nervous was the floor. It was a gruesome mosaic of bones and gems—human femurs, hip bones, and ribs twisted and fused together into a smooth surface, dotted with diamonds and rubies. The bones formed patterns, like skeletal contortionists tumbling together, curling to protect the precious stones—a dance of death and riches.

“Touch nothing,” Hazel said.

“Wasn’t planning on it,” Leo muttered.

Jason scanned the exits. “Which way now?”

For once, Nico looked uncertain. “This should be the room where the priests invoked the most powerful spirits. One of these passages leads deeper into the temple, to the third level and the altar of Hades himself. But which—?”

“That one.” Frank pointed. In a doorway at the opposite end of the room, a ghostly Roman legionnaire beckoned to them. His face was misty and indistinct, but Frank got the feeling the ghost was looking directly at him.

Hazel frowned. “Why that one?”

“You don’t see the ghost?” Frank asked.

“Ghost?” Nico asked.

Okay…if Frank was seeing a ghost that the Underworld kids couldn’t see, something was definitely wrong. He felt like the floor was vibrating underneath him. Then he realized it was vibrating.

“We need to get to that exit,” he said. “Now!”

Hazel almost had to tackle him to restrain him. “Wait, Frank! This floor is not stable, and underneath…well, I’m not sure what’s underneath. I need to scout a safe path.”

“Hurry, then,” he urged.

He drew his bow and herded Hazel along as fast as he dared. Leo scrambled behind him to provide light. The others guarded the rear. Frank could tell he was scaring his friends, but he couldn’t help it. He knew in his gut they had only seconds before…

In front of them, the legionnaire ghost vaporized. The cavern reverberated with monstrous roars—dozens, maybe hundreds of enemies coming from every direction. Frank recognized the throaty bellow of the Earthborn, the screech of gryphons, the guttural war cries of Cyclopes—all sounds he remembered from the Battle of New Rome, amplified underground, echoing in his head even louder than the war god’s voices.

“Hazel, don’t stop!” Nico ordered. He pulled the scepter of Diocletian from his belt. Piper and Jason drew their swords as the monsters spilled into the cavern.

A vanguard of six-armed Earthborn threw a volley of stones that shattered the bone-and-jewel floor like ice. A fissure spread across the center of the room, coming straight toward Leo and Hazel.

No time for caution. Frank tackled his friends, and the three of them skidded across the cavern, landing at the edge of the ghost’s tunnel as rocks and spears flew overhead.

“Go!” Frank yelled. “Go, go!”

Hazel and Leo scrambled into the tunnel, which seemed to be the only one free of monsters. Frank wasn’t sure that was a good sign.

Two meters in, Leo turned. “The others!”

The entire cavern shuddered. Frank looked back and his courage crumbled to dust. Dividing the cavern was a new fifteen-meter-wide chasm, spanned only by two rickety stretches of bone flooring. The bulk of the monster army was on the opposite side, howling in frustration and throwing whatever they could find, including each other. Some attempted to cross the bridges, which creaked and crackled under their weight.

Jason, Piper, and Nico stood on the near side of the chasm, which was good, but they were surrounded by a ring of Cyclopes and hellhounds. More monsters kept pouring in from the side corridors, while gryphons wheeled overhead, undeterred by the crumbling floor.

The three demigods would never make it to the tunnel. Even if Jason tried to fly them, they’d be shot out of the air.

Frank remembered the voice of his ancestor: At the break, you must take charge.

“We have to help them,” Hazel said.

Frank’s mind raced, doing battle calculations. He saw exactly what would happen—where and when his friends would be overwhelmed, how all six of them would die here in this cavern…unless Frank changed the equation.