I probably should have let it go, but I said, "You want to gargle with toilet water again, Clarisse? Close your mouth."

Her friends had to hold her back. They dragged her toward cabin five, while the other campers made way to avoid her flailing feet.

Annabeth stared at me. I couldn't tell whether she was just grossed out or angry at me for dousing her.

"What?" I demanded. "What are you thinking?"

"I'm thinking," she said, "that I want you on my team for capture the flag."

Word of the bathroom incident spread immediately. Wherever I went, campers pointed at me and murmured something about toilet water. Or maybe they were just staring at Annabeth, who was still pretty much dripping wet.

She showed me a few more places: the metal shop (where kids were forging their own swords), the arts-and-crafts room (where satyrs were sandblasting a giant marble statue of a goat-man), and the climbing wall, which actually consisted of two facing walls that shook violently, dropped boulders, sprayed lava, and clashed together if you didn't get to the top fast enough.

Finally we returned to the canoeing lake, where the trail led back to the cabins.

"I've got training to do," Annabeth said flatly. "Dinner's at seven-thirty. Just follow your cabin to the mess hall."

"Annabeth, I'm sorry about the toilets."

"Whatever."

"It wasn't my fault."

She looked at me skeptically, and I realized it was my fault. I'd made water shoot out of the bathroom fixtures. I didn't understand how. But the toilets had responded to me. I had become one with the plumbing.

"You need to talk to the Oracle," Annabeth said.

"Who?"

"Not who. What. The Oracle. I'll ask Chiron."

I stared into the lake, wishing somebody would give me a straight answer for once.

I wasn't expecting anybody to be looking back at me from the bottom, so my heart skipped a beat when I noticed two teenage girls sitting cross-legged at the base of the pier, about twenty feet below. They wore blue jeans and shimmering green T-shirts, and their brown hair floated loose around their shoulders as minnows darted in and out. They smiled and waved as if I were a long-lost friend.

I didn't know what else to do. I waved back.

"Don't encourage them," Annabeth warned. "Naiads are terrible flirts."

"Naiads," I repeated, feeling completely overwhelmed. "That's it. I want to go home now."

Annabeth frowned. "Don't you get it, Percy? You are home. This is the only safe place on earth for kids like us."

"You mean, mentally disturbed kids?"

"I mean not human. Not totally human, anyway. Half-human."

"Half-human and half-what?"

"I think you know."

I didn't want to admit it, but I was afraid I did. I felt a tingling in my limbs, a sensation I sometimes felt when my mom talked about my dad.

"God," I said. "Half-god."

Annabeth nodded. "Your father isn't dead, Percy. He's one of the Olympians."

"That's… crazy."

"Is it? What's the most common thing gods did in the old stories? They ran around falling in love with humans and having kids with them. Do you think they've changed their habits in the last few millennia?"

"But those are just—" I almost said myths again. Then I remembered Chiron's warning that in two thousand years, I might be considered a myth. "But if all the kids here are half-gods—"

"Demigods," Annabeth said. "That's the official term. Or half-bloods."

"Then who's your dad?"

Her hands tightened around the pier railing. I got the feeling I'd just trespassed on a sensitive subject.

"My dad is a professor at West Point," she said. "I haven't seen him since I was very small. He teaches American history."

"He's human."

"What? You assume it has to be a male god who finds a human female attractive? How sexist is that?"

"Who's your mom, then?"

"Cabin six."

"Meaning?"

Annabeth straightened. "Athena. Goddess of wisdom and battle."

Okay, I thought. Why not?

"And my dad?"

"Undetermined," Annabeth said, "like I told you before. Nobody knows."

"Except my mother. She knew."

"Maybe not, Percy. Gods don't always reveal their identities."

"My dad would have. He loved her."

Annabeth gave me a cautious look. She didn't want to burst my bubble. "Maybe you're right. Maybe he'll send a sign. That's the only way to know for sure: your father has to send you a sign claiming you as his son. Sometimes it happens.

"You mean sometimes it doesn't?"

Annabeth ran her palm along the rail. "The gods are busy. They have a lot of kids and they don't always… Well, sometimes they don't care about us, Percy. They ignore us."

I thought about some of the kids I'd seen in the Hermes cabin, teenagers who looked sullen and depressed, as if they were waiting for a call that would never come. I'd known kids like that at Yancy Academy, shuffled off to boarding school by rich parents who didn't have the time to deal with them. But gods should behave better.

"So I'm stuck here," I said. "That's it? For the rest of my life?"

"It depends," Annabeth said. "Some campers only stay the summer. If you're a child of Aphrodite or Demeter, you're probably not a real powerful force. The monsters might ignore you, so you can get by with a few months of summer training and live in the mortal world the rest of the year. But for some of us, it's too dangerous to leave. We're year-rounders. In the mortal world, we attract monsters. They sense us. They come to challenge us. Most of the time, they'll ignore us until we're old enough to cause trouble—about ten or eleven years old, but after that, most demigods either make their way here, or they get killed off. A few manage to survive in the outside world and become famous. Believe me, if I told you the names, you'd know them. Some don't even realize they're demigods. But very, very few are like that."

"So monsters can't get in here?"

Annabeth shook her head. "Not unless they're intentionally stocked in the woods or specially summoned by somebody on the inside."

"Why would anybody want to summon a monster?"

"Practice fights. Practical jokes."

"Practical jokes?"

"The point is, the borders are sealed to keep mortals and monsters out. From the outside, mortals look into the valley and see nothing unusual, just a strawberry farm."

"So… you're a year-rounder?"

Annabeth nodded. From under the collar of her T-shirt she pulled a leather necklace with five clay beads of different colors. It was just like Luke's, except Annabeth's also had a big gold ring strung on it, like a college ring.

"I've been here since I was seven," she said. "Every August, on the last day of summer session, you get a bead for surviving another year. I've been here longer than most of the counselors, and they're all in college."

"Why did you come so young?"

She twisted the ring on her necklace. "None of your business."

"Oh." I stood there for a minute in uncomfortable silence. "So… I could just walk out of here right now if I wanted to?"

"It would be suicide, but you could, with Mr. D's or Chiron's permission. But they wouldn't give permission until the end of the summer session unless…"

"Unless?"

"You were granted a quest. But that hardly ever happens. The last time…"

Her voice trailed off. I could tell from her tone that the last time hadn't gone well.

"Back in the sick room," I said, "when you were feeding me that stuff—"

"Ambrosia."

"Yeah. You asked me something about the summer solstice."

Annabeth's shoulders tensed. "So you do know something?"

"Well… no. Back at my old school, I overheard Grover and Chiron talking about it. Grover mentioned the summer solstice. He said something like we didn't have much time, because of the deadline. What did that mean?"