"You're my son," she said miserably. "I can't just . . ."

I could tell I'd have to push her harder if I wanted her to agree, but I didn't want to. I remembered poor Ms. Castellan in her kitchen, waiting for her son to come home. And I realized how lucky I was. My mom had always been there for me, always tried to make things normal for me, even with the gods and monsters and stuff. She put up with me going off on adventures, but now I was asking her blessing to do something that would probably get me killed.

I locked eyes with Paul, and some kind of understanding passed between us.

"Sally." He put his hand over my mother's hands. "I can't claim to know what you and Percy have been going through all these years. But it sounds to me . . . it sounds like Percy is doing something noble. I wish I had that much courage."

I got a lump in my throat. I didn't get compliments like that too much.

My mom stared at her lemonade. She looked like she was trying not to cry. I thought about what Hestia had said, about how hard it was to yield, and I figured maybe my mom was finding that out.

"Percy," she said, "I give you my blessing."

I didn't feel any different. No magic glow lit the kitchen or anything.

I glanced at Nico.

He looked more anxious than ever, but he nodded. "It's time."

"Percy," my mom said. "One last thing. If you . . . if you survive this fight with Kronos, send me a sign." She rummaged through her purse and handed me her cell phone.

"Mom," I said, "you know demigods and phones—"

"I know," she said. "But just in case. If you're not able to call . . . maybe a sign that I could see from anywhere in Manhattan. To let me know you're okay."

"Like Theseus," Paul suggested. "He was supposed to raise white sails when he came home to Athens."

"Except he forgot," Nico muttered. "And his father jumped off the palace roof in despair. But other than that, it was a great idea."

"What about a flag or a flare?" my mom said. "From Olympus—the Empire State Building."

"Something blue," I said.

We'd had a running joke for years about blue food. It was my favorite color, and my mom went out of her way to humor me. Every year my birthday cake, my Easter basket, my Christmas candy canes always had to be blue.

"Yes," my mom agreed. "I'll watch for a blue signal. And I'll try to avoid jumping off palace roofs."

She gave me one last hug. I tried not to feel like I was saying good-bye. I shook hands with Paul. Then Nico and I walked to the kitchen doorway and looked at Mrs. O'Leary.

"Sorry, girl," I said. "Shadow travel time again."

She whimpered and crossed her paws over her snout.

"Where now?" I asked Nico. "Los Angeles?"

"No need," he said. "There's a closer entrance to the Underworld."

We emerged in Central Park just north of the Pond. Mrs. O'Leary looked pretty tired as she limped over to a cluster of boulders. She started sniffing around, and I was afraid she might mark her territory, but Nico said, "It's okay. She just smells the way home."

I frowned. "Through the rocks?"

"The Underworld has two major entrances," Nico said. "You know the one in L.A."

"Charon's ferry."

Nico nodded. "Most souls go that way, but there's a smaller path, harder to find. The Door of Orpheus."

"The dude with the harp."

"Dude with the lyre," Nico corrected. "But yeah, him. He used his music to charm the earth and open a new path into the Underworld. He sang his way right into Hades's palace and almost got away with his wife's soul."

I remembered the story. Orpheus wasn't supposed to look behind him when he was leading his wife back to the world, but of course he did. It was one of those typical "and-so-they-died/the-end" stories that always made us feel warm and fuzzy.

"So this is the Door of Orpheus." I tried to be impressed, but it still looked like a pile of rocks to me. "How does it open?"

"We need music," Nico said. "How's your singing?"

"Um, no. Can't you just, like, tell it to open? You're the son of Hades and all."

"It's not so easy. We need music."

I was pretty sure if I tried to sing, all I would cause was an avalanche.

"I have a better idea." I turned and called, "GROVER!"

We waited for a long time. Mrs. O'Leary curled up and took a nap. I could hear the crickets in the woods and an owl hooting. Traffic hummed along Central Park West. Horse hooves clopped down a nearby path, maybe a mounted police patrol. I was sure they'd love to find two kids hanging out in the park at one in the morning.

"It's no good," Nico said at last.

But I had a feeling. My empathy link was really tingling for the first time in months, which either meant a whole lot of people had suddenly switched on the Nature Channel, or Grover was close.

I shut my eyes and concentrated. Grover.

I knew he was somewhere in the park. Why couldn't I sense his emotions? All I got was a faint hum in the base of my skull.

Grover, I thought more insistently.

Hmm-hmmmm, something said.

An image came into my head. I saw a giant elm tree deep in the woods, well off the main paths. Gnarled roots laced the ground, making a kind of bed. Lying in it with his arms crossed and his eyes closed was a satyr. At first I couldn't be sure it was Grover. He was covered in twigs and leaves, like he'd been sleeping there a long time. The roots seemed to be shaping themselves around him, slowly pulling him into the earth.

Grover, I said. Wake up.

Unnnh—zzzzz.

Dude, you're covered in dirt. Wake up!

Sleepy, his mind murmured.

FOOD, I suggested. PANCAKES!

His eyes shot open. A blur of thoughts filled my head like he was suddenly on fast-forward. The image shattered, and I almost fell over.

"What happened?" Nico asked.

"I got through. He's . . . yeah. He's on his way."

A minute later, the tree next to us shivered. Grover fell out of the branches, right on his head.

"Grover!" I yelled.

"Woof!" Mrs. O'Leary looked up, probably wondering if we were going to play fetch with the satyr.

"Blah-haa-haa!" Grover bleated.

"You okay, man?"

"Oh, I'm fine." He rubbed his head. His horns had grown so much they poked an inch above his curly hair. "I was at the other end of the park. The dryads had this great idea of passing me through the trees to get me here. They don't understand height very well."

He grinned and got to his feet—well, his hooves, actually. Since last summer, Grover had stopped trying to disguise himself as human. He never wore a cap or fake feet anymore. He didn't even wear jeans, since he had furry goat legs from the waist down. His T-shirt had a picture from that book Where the Wild Things Are. It was covered with dirt and tree sap. His goatee looked fuller, almost manly (or goatly?), and he was as tall as me now.

"Good to see you, G-man," I said. "You remember Nico."

Grover nodded at Nico, then he gave me a big hug. He smelled like fresh-mown lawns.

"Perrrrcy!" he bleated. "I missed you! I miss camp. They don't serve very good enchiladas in the wilderness."

"I was worried," I said. "Where've you been the last two months?"

"The last two—" Grover's smile faded. "The last two months? What are you talking about?"

"We haven't heard from you," I said. "Juniper's worried. We sent Iris-messages, but—"

"Hold on." He looked up at the stars like he was trying to calculate his position. "What month is this?"

"August."

The color drained from his face. "That's impossible. It's June. I just lay down to take a nap and . . ." He grabbed my arms. "I remember now! He knocked me out. Percy, we have to stop him!"