Grover looked down at the naiads. "Mr. D suspended judgment. He said I hadn't failed or succeeded with you yet, so our fates were still tied together. If you got a quest and I went along to protect you, and we both came back alive, then maybe he'd consider the job complete."

My spirits lifted. "Well, that's not so bad, right?"

"Blaa-ha-ha! He might as well have transferred me to stable-cleaning duty. The chances of you getting a quest... and even if you did, why would you want me along?"

"Of course I'd want you along!"

Grover stared glumly into the water. "Basket-weaving ... Must be nice to have a useful skill."

I tried to reassure him that he had lots of talents, but that just made him look more miserable. We talked about canoeing and swordplay for a while, then debated the pros and cons of the different gods. Finally, I asked him about the four empty cabins.

"Number eight, the silver one, belongs to Artemis," he said. "She vowed to be a maiden forever. So of course, no kids. The cabin is, you know, honorary. If she didn't have one, she'd be mad."

"Yeah, okay. But the other three, the ones at the end. Are those the Big Three?"

Grover tensed. We were getting close to a touchy subject. "No. One of them, number two, is Hera's," he said. "That's another honorary thing. She's the goddess of marriage, so of course she wouldn't go around having affairs with mortals. That's her husband's job. When we say the Big Three, we mean the three powerful brothers, the sons of Kronos."

"Zeus, Poseidon, Hades."

"Right. You know. After the great battle with the Titans, they took over the world from their dad and drew lots to decide who got what."

"Zeus got the sky," I remembered. "Poseidon the sea, Hades the Underworld."

"Uh-huh."

"But Hades doesn't have a cabin here."

"No. He doesn't have a throne on Olympus, either. He sort of does his own thing down in the Underworld. If he did have a cabin here ..." Grover shuddered. "Well, it wouldn't be pleasant. Let's leave it at that."

"But Zeus and Poseidon—they both had, like, a bazillion kids in the myths. Why are their cabins empty?"

Grover shifted his hooves uncomfortably. "About sixty years ago, after World War II, the Big Three agreed they wouldn't sire any more heroes. Their children were just too powerful. They were affecting the course of human events too much, causing too much carnage. World War II, you know, that was basically a fight between the sons of Zeus and Poseidon on one side, and the sons of Hades on the other. The winning side, Zeus and Poseidon, made Hades swear an oath with them: no more affairs with mortal women. They all swore on the River Styx."

Thunder boomed.. . . . . ..

I said, "That's the most serious oath you can make."

Grover nodded.

"And the brothers kept their word—no kids?"

Grover's face darkened. "Seventeen years ago, Zeus fell off the wagon. There was this TV starlet with a big fluffy eighties hairdo—he just couldn't help himself. When their child was born, a little girl named Thalia .. . well, the River Styx is serious about promises. Zeus himself got off easy because he's immortal, but he brought a terrible fate on his daughter."

"But that isn't fair.' It wasn't the little girl's fault."

Grover hesitated. "Percy, children of the Big Three have powers greater than other half-bloods. They have a strong aura, a scent that attracts monsters. When Hades found out about the girl, he wasn't too happy about Zeus breaking his oath. Hades let the worst monsters out of Tartarus to torment Thalia. A satyr was assigned to be her keeper when she was twelve, but there was nothing he could do. He tried to escort her here with a couple of other half-bloods she'd befriended. They almost made it. They got all the way to the top of that hill."

He pointed across the valley, to the pine tree where I'd fought the minotaur. "All three Kindly Ones were after them, along with a horde of hellhounds. They were about to be overrun when Thalia told her satyr to take the other two half-bloods to safety while she held off the monsters. She was wounded and tired, and she didn't want to live like a hunted animal. The satyr didn't want to leave her, but he couldn't change her mind, and he had to protect the others. So Thalia made her final stand alone, at the top of that hill. As she died, Zeus took pity on her. He turned her into that pine tree. Her spirit still helps protect the borders of the valley. That's why the hill is called Half-Blood Hill."

I stared at the pine in the distance.

The story made me feel hollow, and guilty too. A girl my age had sacrificed herself to save her friends. She had faced a whole army of monsters. Next to that, my victory over the Minotaur didn't seem like much. I wondered, if I'd acted differently, could I have saved my mother?

"Grover," I said, "have heroes really gone on quests to the Underworld?"

"Sometimes," he said. "Orpheus. Hercules. Houdini."

"And have they ever returned somebody from the dead?"

"No. Never. Orpheus came close... . Percy, you're not seriously thinking—"

"No," I lied. "I was just wondering. So ... a satyr is always assigned to guard a demigod?"

Grover studied me warily. I hadn't persuaded him that I'd really dropped the Underworld idea. "Not always. We go undercover to a lot of schools. We try to sniff out the half-bloods who have the makings of great heroes. If we find one with a very strong aura, like a child of the Big Three, we alert Chiron. He tries to keep an eye on them, since they could cause really huge problems."

"And you found me. Chiron said you thought I might be something special."

Grover looked as if I'd just led him into a trap. "I didn't... Oh, listen, don't think like that. If you were—you know—you'd never ever be allowed a quest, and I'd never get my license. You're probably a child of Hermes. Or maybe even one of the minor gods, like Nemesis, the god of revenge. Don't worry, okay?"

I got the idea he was reassuring himself more than me.

That night after dinner, there was a lot more excitement than usual.

At last, it was time for capture the flag.

When the plates were cleared away, the conch horn sounded and we all stood at our tables.

Campers yelled and cheered as Annabeth and two of her siblings ran into the pavilion carrying a silk banner. It was about ten feet long, glistening gray, with a painting of a barn owl above an olive tree. From the opposite side of the pavilion, Clarisse and her buddies ran in with another banner, of identical size, but gaudy red, painted with a bloody spear and a boar's head.

I turned to Luke and yelled over the noise, "Those are the flags?"

"Yeah."

"Ares and Athena always lead the teams?"

"Not always," he said. "But often."

"So, if another cabin captures one, what do you do— repaint the flag?"

He grinned. "You'll see. First we have to get one."

"Whose side are we on?"

He gave me a sly look, as if he knew something I didn't. The scar on his face made him look almost evil in the torchlight. "We've made a temporary alliance with Athena. Tonight, we get the flag from Ares. And you are going to help."

The teams were announced. Athena had made an alliance with Apollo and Hermes, the two biggest cabins. Apparently, privileges had been traded—shower times, chore schedules, the best slots for activities—in order to win support.

Ares had allied themselves with everybody else: Dionysus, Demeter, Aphrodite, and Hephaestus. From what I'd seen, Dionysus's kids were actually good athletes, but there were only two of them. Demeter's kids had the edge with nature skills and outdoor stuff but they weren't very aggressive. Aphrodite's sons and daughters I wasn't too worried about. They mostly sat out every activity and checked their reflections in the lake and did their hair and gossiped. Hephaestus's kids weren't pretty, and there were only four of them, but they were big and burly from working in the metal shop all day. They might be a problem. That, of course, left Ares's cabin: a dozen of the biggest, ugliest, meanest kids on Long Island, or anywhere else on the planet.

Chiron hammered his hoof on the marble.

"Heroes!" he announced. "You know the rules. The creek is the boundary line. The entire forest is fair game. All magic items are allowed. The banner must be prominently displayed, and have no more than two guards. Prisoners may be disarmed, but may not be bound or gagged. No killing or maiming is allowed. I will serve as referee and battlefield medic. Arm yourselves!"

He spread his hands, and the tables were suddenly covered with equipment: helmets, bronze swords, spears, oxhide shields coated in metal.

"Whoa," I said. "We're really supposed to use these?"

Luke looked at me as if I were crazy. "Unless you want to get skewered by your friends in cabin five. Here—Chiron thought these would fit. You'll be on border patrol."

My shield was the size of an NBA backboard, with a big caduceus in the middle. It weighed about a million pounds. I could have snowboarded on it fine, but I hoped nobody seriously expected me to run fast. My helmet, like all the helmets on Athena's side, had a blue horsehair plume on top. Ares and their allies had red plumes.

Annabeth yelled, "Blue team, forward!"

We cheered and shook our swords and followed her down the path to the south woods. The red team yelled taunts at us as they headed off toward the north.

I managed to catch up with Annabeth without tripping over my equipment. "Hey."

She kept marching.

"So what's the plan?" I asked. "Got any magic items you can loan me?"

Her hand drifted toward her pocket, as if she were afraid I'd stolen something.

"Just watch Clarisse's spear," she said. "You don't want that thing touching you. Otherwise, don't worry. We'll take the banner from Ares. Has Luke given you your job?"

"Border patrol, whatever that means."

"It's easy. Stand by the creek, keep the reds away. Leave the rest to me. Athena always has a plan."

She pushed ahead, leaving me in the dust.

"Okay," I mumbled. "Glad you wanted me on your team."

It was a warm, sticky night. The woods were dark, with fireflies popping in and out of view. Annabeth stationed me next to a little creek that gurgled over some rocks, then she and the rest of the team scattered into the trees.

Standing there alone, with my big blue-feathered helmet and my huge shield, I felt like an idiot. The bronze sword, like all the swords I'd tried so far, seemed balanced wrong. The leather grip pulled on my hand like a bowling ball.

There was no way anybody would actually attack me, would they? I mean, Olympus had to have liability issues, right?

Far away, the conch horn blew. I heard whoops and yells in the woods, the clanking of metal, kids fighting. A blue-plumed ally from Apollo raced past me like a deer, leaped through the creek, and disappeared into enemy territory.

Great, I thought. I'll miss all the fun, as usual.

Then I heard a sound that sent a chill up my spine, a low canine growl, somewhere close by.

I raised my shield instinctively; I had the feeling something was stalking me.

Then the growling stopped. I felt the presence retreating.