"Don't worry," Annabeth told me. "Mortal police could never find us." But she didn't sound so sure.

The rest of the day I spent alternately pacing the length of the train (because I had a really hard time sitting still) or looking out the windows.

Once, I spotted a family of centaurs galloping across a wheat field, bows at the ready, as they hunted lunch. The little boy centaur, who was the size of a second-grader on a pony, caught my eye and waved. I looked around the passenger car, but nobody else had noticed. The adult riders all had their faces buried in laptop computers or magazines.

Another time, toward evening, I saw something huge moving through the woods. I could've sworn it was a lion, except that lions don't live wild in America, and this thing was the size of a Hummer. Its fur glinted gold in the evening light. Then it leaped through the trees and was gone.

Our reward money for returning Gladiola the poodle had only been enough to purchase tickets as far as Denver. We couldn't get berths in the sleeper car, so we dozed in our seats. My neck got stiff. I tried not to drool in my sleep, since Annabeth was sitting right next to me.

Grover kept snoring and bleating and waking me up. Once, he shuffled around and his fake foot fell off. Annabeth and I had to stick it back on before any of the other passengers noticed.

"So," Annabeth asked me, once we'd gotten Grover's sneaker readjusted. "Who wants your help?"

"What do you mean?"

"When you were asleep just now, you mumbled, 'I won't help you.' Who were you dreaming about?"

I was reluctant to say anything. It was the second time I'd dreamed about the evil voice from the pit. But it bothered me so much I finally told her.

Annabeth was quiet for a long time. "That doesn't sound like Hades. He always appears on a black throne, and he never laughs."

"He offered my mother in trade. Who else could do that?"

"I guess ... if he meant, 'Help me rise from the Underworld.' If he wants war with the Olympians. But why ask you to bring him the master bolt if he already has it?"

I shook my head, wishing I knew the answer. I thought about what Grover had told me, that the Furies on the bus seemed to have been looking for something.

Where is it? Where?

Maybe Grover sensed my emotions. He snorted in his sleep, muttered something about vegetables, and turned his head.

Annabeth readjusted his cap so it covered his horns. "Percy, you can't barter with Hades. You know that, right? He's deceitful, heartless, and greedy. I don't care if his Kindly Ones weren't as aggressive this time—"

"This time?" I asked. "You mean you've run into them before?"

Her hand crept up to her necklace. She fingered a glazed white bead painted with the image of a pine tree, one of her clay end-of-summer tokens. "Let's just say I've got no love for the Lord of the Dead. You can't be tempted to make a deal for your mom."

"What would you do if it was your dad?"

"That's easy," she said. "I'd leave him to rot."

"You're not serious?"

Annabeth's gray eyes fixed on me. She wore the same expression she'd worn in the woods at camp, the moment she drew her sword against the hellhound. "My dad's resented me since the day I was born, Percy," she said. "He never wanted a baby. When he got me, he asked Athena to take me back and raise me on Olympus because he was too busy with his work. She wasn't happy about that. She told him heroes had to be raised by their mortal parent."

"But how ... I mean, I guess you weren't born in a hospital...."

"I appeared on my father's doorstep, in a golden cradle, carried down from Olympus by Zephyr the West Wind. You'd think my dad would remember that as a miracle, right? Like, maybe he'd take some digital photos or something. But he always talked about my arrival as if it were the most inconvenient thing that had ever happened to him. When I was five he got married and totally forgot about Athena. He got a 'regular' mortal wife, and had two 'regular' mortal kids, and tried to pretend I didn't exist."

I stared out the train window. The lights of a sleeping town were drifting by. I wanted to make Annabeth feel better, but I didn't know how.

"My mom married a really awful guy," I told her. "Grover said she did it to protect me, to hide me in the scent of a human family. Maybe that's what your dad was thinking."

Annabeth kept worrying at her necklace. She was pinching the gold college ring that hung with the beads. It occurred to me that the ring must be her father's. I wondered why she wore it if she hated him so much.

"He doesn't care about me," she said. "His wife—my stepmom—treated me like a freak. She wouldn't let me play with her children. My dad went along with her. Whenever something dangerous happened—you know, something with monsters—they would both look at me resentfully, like, 'How dare you put our family at risk.' Finally, I took the hint. I wasn't wanted. I ran away."

"How old were you?"

"Same age as when I started camp. Seven."

"But ... you couldn't have gotten all the way to Half-Blood Hill by yourself."

"Not alone, no. Athena watched over me, guided me toward help. I made a couple of unexpected friends who took care of me, for a short time, anyway."

I wanted to ask what happened, but Annabeth seemed lost in sad memories. So I listened to the sound of Grover snoring and gazed out the train windows as the dark fields of Ohio raced by.

Toward the end of our second day on the train, June 13, eight days before the summer solstice, we passed through some golden hills and over the Mississippi River into St. Louis. Annabeth craned her neck to see the Gateway Arch, which looked to me like a huge shopping bag handle stuck on the city.

"I want to do that," she sighed.

"What?" I asked.

"Build something like that. You ever see the Parthenon, Percy?"

"Only in pictures."

"Someday, I'm going to see it in person. I'm going to build the greatest monument to the gods, ever. Something that'll last a thousand years."

I laughed. "You? An architect?"

I don't know why, but I found it funny. Just the idea of Annabeth trying to sit quietly and draw all day.

Her cheeks flushed. "Yes, an architect. Athena expects her children to create things, not just tear them down, like a certain god of earthquakes I could mention."

I watched the churning brown water of the Mississippi below.

"Sorry," Annabeth said. "That was mean."

"Can't we work together a little?" I pleaded. "I mean, didn't Athena and Poseidon ever cooperate?"

Annabeth had to think about it. "I guess ... the chariot," she said tentatively. "My mom invented it, but Poseidon created horses out of the crests of waves. So they had to work together to make it complete."

"Then we can cooperate, too. Right?"

We rode into the city, Annabeth watching as the Arch disappeared behind a hotel.

"I suppose," she said at last.

We pulled into the Amtrak station downtown. The intercom told us we'd have a three-hour layover before departing for Denver.

Grover stretched. Before he was even fully awake, he said, "Food."

"Come on, goat boy," Annabeth said. "Sightseeing."

"Sightseeing?"

"The Gateway Arch," she said. "This may be my only chance to ride to the top. Are you coming or not?"

Grover and I exchanged looks.

I wanted to say no, but I figured that if Annabeth was going, we couldn't very well let her go alone.

Grover shrugged. "As long as there's a snack bar without monsters."

The Arch was about a mile from the train station. Late in the day the lines to get in weren't that long. We threaded our way through the underground museum, looking at covered wagons and other junk from the 1800s. It wasn't all that thrilling, but Annabeth kept telling us interesting facts about how the Arch was built, and Grover kept passing me jelly beans, so I was okay.

I kept looking around, though, at the other people in line. "You smell anything?" I murmured to Grover.

He took his nose out of the jelly-bean bag long enough to sniff. "Underground," he said distastefully. "Underground air always smells like monsters. Probably doesn't mean anything."

But something felt wrong to me. I had a feeling we shouldn't be here.

"Guys," I said. "You know the gods' symbols of power?"

Annabeth had been in the middle of reading about the construction equipment used to build the Arch, but she looked over. "Yeah?"

"Well, Hade—"

Grover cleared his throat. "We're in a public place.... You mean, our friend downstairs?"

"Um, right," I said. "Our friend way downstairs. Doesn't he have a hat like Annabeth's?"

"You mean the Helm of Darkness," Annabeth said. "Yeah, that's his symbol of power. I saw it next to his seat during the winter solstice council meeting."

"He was there?" I asked.

She nodded. "It's the only time he's allowed to visit Olympus—the darkest day of the year. But his helm is a lot more powerful than my invisibility hat, if what I've heard is true...."

"It allows him to become darkness," Grover confirmed. "He can melt into shadow or pass through walls. He can't be touched, or seen, or heard. And he can radiate fear so intense it can drive you insane or stop your heart. Why do you think all rational creatures fear the dark?"

"But then ... how do we know he's not here right now, watching us?" I asked.

Annabeth and Grover exchanged looks.

"We don't," Grover said.

"Thanks, that makes me feel a lot better," I said. "Got any blue jelly beans left?"

I'd almost mastered my jumpy nerves when I saw the tiny little elevator car we were going to ride to the top of the Arch, and I knew I was in trouble. I hate confined places. They make me nuts.

We got shoehorned into the car with this big fat lady and her dog, a Chihuahua with a rhinestone collar. I figured maybe the dog was a seeing-eye Chihuahua, because none of the guards said a word about it.

We started going up, inside the Arch. I'd never been in an elevator that went in a curve, and my stomach wasn't too happy about it.

"No parents?" the fat lady asked us.

She had beady eyes; pointy, coffee-stained teeth; a floppy denim hat, and a denim dress that bulged so much, she looked like a blue-jean blimp.

"They're below," Annabeth told her. "Scared of heights."

"Oh, the poor darlings."

The Chihuahua growled. The woman said, "Now, now, sonny. Behave." The dog had beady eyes like its owner, intelligent and vicious.

I said, "Sonny. Is that his name?"

"No," the lady told me.

She smiled, as if that cleared everything up.

At the top of the Arch, the observation deck reminded me of a tin can with carpeting. Rows of tiny windows looked out over the city on one side and the river on the other. The view was okay, but if there's anything I like less than a confined space, it's a confined space six hundred feet in the air. I was ready to go pretty quick.

Annabeth kept talking about structural supports, and how she would've made the windows bigger, and designed a see-through floor. She probably could've stayed up there for hours, but luckily for me the park ranger announced that the observation deck would be closing in a few minutes.