Nico was only ten, or maybe eleven by now, but he looked older. His hair had grown longer. It was shaggy and almost touched his shoulders. His eyes were dark. His olive skin had turned paler. He wore ripped black jeans and a battered aviator’s jacket that was several sizes too big, unzipped over a black shirt. His face was grimy, his eyes a little wild. He looked like a kid who’d been living on the streets.

I waited for him to look at me. No doubt he’d get crazy angry, start accusing me of letting his sister die. But he didn’t seem to notice me.

I stayed quiet, not daring to move. If he hadn’t sent this Iris-message, who had?

Nico tossed another trading card into the blue flames. “Useless,” he muttered. “I can’t believe I ever liked this stuff.”

“A childish game, master,” another voice agreed. It seemed to come from near the fire, but I couldn’t see who was talking.

Nico stared across the river. On the far shore was black beach shrouded in haze. I recognized it: the Underworld. Nico was camping at the edge of the river Styx.

“I’ve failed,” he muttered. “There’s no way to get her back.”

The other voice kept silent.

Nico turned toward it doubtfully. “Is there? Speak.”

Something shimmered. I thought it was just firelight. Then I realized it was the form of a man—a wisp of blue smoke, a shadow. If you looked at him head-on, he wasn’t there. But if you looked out of the corner of your eye, you could make out his shape. A ghost.

“It has never been done,” the ghost said. “But there may be a way.”

“Tell me,” Nico commanded. His eyes shined with a fierce light.

“An exchange,” the ghost said. “A soul for a soul.”

“I’ve offered!”

“Not yours,” the ghost said. “You cannot offer your father a soul he will eventually collect anyway. Nor will he be anxious for the death of his son. I mean a soul that should have died already. Someone who has cheated death.”

Nico’s face darkened. “Not that again. You’re talking about murder.”

“I’m talking about justice,” the ghost said. “Vengeance.”

“Those are not the same thing.”

The ghost laughed dryly. “You will learn differently as you get older.”

Nico stared at the flames. “Why can’t I at least summon her? I want to talk to her. She would…she would help me.”

“I will help you,” the ghost promised. “Have I not saved you many times? Did I not lead you through the maze and teach you to use your powers? Do you want revenge for your sister or not?”

I didn’t like the ghost’s tone of voice. He reminded me of a kid at my old school, a bully who used to convince other kids to do stupid things like steal lab equipment and vandalize the teachers’ cars. The bully never got in trouble himself, but he got tons of other kids suspended.

Nico turned from the fire so the ghost couldn’t see him, but I could. A tear traced its way down his face. “Very well. You have a plan?”

“Oh, yes,” the ghost said, sounding quite pleased. “We have many dark roads to travel. We must start—”

The image shimmered. Nico vanished. The woman’s voice from the mist said, Please deposit one drachma for another five minutes.

There were no other coins in the fountain. I grabbed for my pockets, but I was wearing pajamas. I lunged for the nightstand to check for spare change, but the Iris-message had already blinked out, and the room went dark again. The connection was broken.

I stood in the middle of the cabin, listening to the gurgle of the saltwater fountain and the ocean waves outside.

Nico was alive. He was trying to bring his sister back from the dead. And I had a feeling I knew what soul he wanted to exchange—someone who had cheated death. Vengeance.

Nico di Angelo would come looking for me.

THREE

WE PLAY TAG WITH SCORPIONS

The next morning there was a lot of excitement at breakfast.

Apparently around three in the morning an Aethiopian drakon had been spotted at the borders of camp. I was so exhausted I slept right through the noise. The magical boundaries had kept the monster out, but it prowled the hills, looking for weak spots in our defenses, and it didn’t seem anxious to go away until Lee Fletcher from Apollo’s cabin led a couple of his siblings in pursuit. After a few dozen arrows lodged in the chinks of the drakon’s armor, it got the message and withdrew.

“It’s still out there,” Lee warned us during announcements. “Twenty arrows in its hide, and we just made it mad. The thing was thirty feet long and bright green. It’s eyes—” he shuddered.

“You did well, Lee,” Chiron patted him on the shoulder. “Everyone stay alert, but stay calm. This has happened before.”

“Aye,” Quintus said from the head table. “And it will happen again. More and more frequently.”

The campers murmured among themselves.

Everyone knew the rumors: Luke and his army of monsters were planning an invasion of the camp. Most of us expected it to happen this summer, but no one knew how or when. It didn’t help that our attendance was down. We only had about eighty campers. Three years ago, when I’d started, there had been more than a hundred. Some had died. Some had joined Luke. Some had just disappeared.

“This is a good reason for new war games, “Quintus continued, a glint in his eyes. “We’ll see how you all do with that tonight.”

“Yes…” Chiron said. “Well, enough announcements. Let us bless this meal and eat.” He raised his goblet. “To the gods.”

We all raised our glasses and repeated the blessing.

Tyson and I took our plates to the bronze brazier and scraped a portion of our food into the flames. I hoped the gods liked raisin toast and Froot Loops.

“Poseidon,” I said. Then I whispered, “Help me with Nico, and Luke, and Grover’s problem…”

There was so much to worry about I could’ve stood there all morning, but I headed back to the table.

Once everyone was eating, Chiron and Grover came over to visit. Grover was bleary-eyed. His shirt was inside out. He slid his plate onto the table and slumped next to me.

Tyson shifted uncomfortably. “I will go…um…polish my fish ponies.”

He lumbered off, leaving his breakfast half-eaten.

Chiron tried for a smile. He probably wanted to look reassuring, but in centaur form he towered over me, casting a shadow across the table. “Well, Percy, how did you sleep?”

“Uh, fine.” I wondered why he asked that. Was it possible he knew something about the weird Iris-message I’d gotten?

“I brought Grover over,” Chiron said, “because I thought you two might want to, ah, discuss matters. Now if you’ll excuse me, I have some Iris-messages to send. I’ll see you later in the day.” He gave Grover a meaningful look, then trotted out of the pavilion.”

“What’s he talking about?” I asked Grover.

Grover chewed his eggs. I could tell he was distracted, because he bit the tines of his fork and chewed those down, too. “He wants you to convince me,” he mumbled.

Somebody else slid next to me on the bench: Annabeth.

“I’ll tell you what it’s about,” she said. “The Labyrinth.”

It was hard to concentrate on what she was saying, because everybody in the dining pavilion was stealing glances at us and whispering. And Annabeth was right next to me. I mean right next to me.

“You’re not supposed to be here,” I said.

“We need to talk,” she insisted.

“But the rules…”

She knew as well as I did that campers weren’t allowed to switch tables. Satyrs were different. They weren’t really demigods. But the half-bloods had to sit with their cabins. I wasn’t even sure what the punishment was for switching tables. I’d never seen it happen. If Mr. D had been here, he probably would’ve strangled Annabeth with magical grapevines or something, but Mr. D wasn’t here. Chiron had already left the pavilion. Quintus looked over and raised an eyebrow, but he didn’t say anything.

“Look,” Annabeth said, “Grover is in trouble. There’s only one way we can figure to help him. It’s the Labyrinth. That’s what Clarisse and I have been investigating.”

I shifted my weight, trying to think clearly. “You mean the maze where they kept the Minotaur, back in the old days?”

“Exactly,” Annabeth said.

“So…it’s not under the king’s palace in Crete anymore,” I guessed. “The Labyrinth is under some building in America.”

See? It only took me a few years to figure things out. I knew that important places moved around with Western Civilization, like Mount Olympus being over the Empire State building, and the Underworld entrance being in Los Angeles. I was feeling pretty proud of myself.

Annabeth rolled her eyes. “Under a building? Please, Percy. The Labyrinth is huge. It wouldn’t fit under a single city, much less a single building.”

I thought about my dream of Nico at the River Styx. “So…is the Labyrinth part of the Underworld?”

“No.” Annabeth frowned. “Well, there may be passages from the Labyrinth down into the Underworld. I’m not sure. But the Underworld is way, way down. The Labyrinth is right under the surface of the mortal world, kind of like a second skin. It’s been growing for thousands of years, lacing its way under Western cities, connecting everything together underground. You can get anywhere through the Labyrinth.”

“If you don’t get lost,” Grover muttered. “And die a horrible death.”

“Grover, there has to be a way,” Annabeth said. I got the feeling they’d had this conversation before. “Clarisse lived.”

“Barely!” Grover said. “And the other guy—”

“He was driven insane. He didn’t die.”

“Oh, joy.” Grover’s lower lip quivered. “That makes me feel much better.”

“Whoa,” I said. “Back up. What’s this about Clarisse and a crazy guy?”

Annabeth glanced over toward the Ares table. Clarisse was watching us like she knew what we were talking about, but then she fixed her eyes on her breakfast plate.

“Last year,” Annabeth said, lowering her voice, “Clarisse went on a mission for Chiron.”

“I remember,” I said. “It was secret.”

Annabeth nodded. Despite how serious she was acting, I was happy she wasn’t mad at me anymore. And I kind of liked the fact that she’d broken the rules to come sit next to me.

“It was secret,” Annabeth agreed, “because she found Chris Rodriguez.”

“The guy from the Hermes cabin?” I remembered him from two years ago. We’d eavesdropped on Chris Rodriguez aboard Luke’s ship, the Princess Andromeda. Chris was one of the half-bloods who’d abandoned camp and joined the Titan Army.

“Yeah,” Annabeth said. “Last summer he just appeared in Phoenix, Arizona, near Clarisse’s mom’s house.”