"This is difficult," he stressed. "I've had it used against me. No laughing at Percy, now. Most swordsmen have to work years to master this technique."

He demonstrated the move on me in slow motion. Sure enough, the sword clattered out of my hand.

"Now in real time," he said, after I'd retrieved my weapon. "We keep sparring until one of us pulls it off. Ready, Percy?"

I nodded, and Luke came after me. Somehow, I kept him from getting a shot at the hilt of my sword. My senses opened up. I saw his attacks coming. I countered. I stepped forward and tried a thrust of my own. Luke deflected it easily, but I saw a change in his face. His eyes narrowed, and he started to press me with more force.

The sword grew heavy in my hand. The balance wasn't right. I knew it was only a matter of seconds before Luke took me down, so I figured, What the heck?

I tried the disarming maneuver.

My blade hit the base of Luke's and I twisted, putting my whole weight into a downward thrust.

Clang.

Luke's sword rattled against the stones. The tip of my blade was an inch from his undefended chest.

The other campers were silent.

I lowered my sword. "Um, sorry."

For a moment, Luke was too stunned to speak.

"Sorry?" His scarred face broke into a grin. "By the gods, Percy, why are you sorry? Show me that again!"

I didn't want to. The short burst of manic energy had completely abandoned me. But Luke insisted.

This time, there was no contest. The moment our swords connected, Luke hit my hilt and sent my weapon skidding across the floor.

After a long pause, somebody in the audience said, "Beginner's luck?"

Luke wiped the sweat off his brow. He appraised at me with an entirely new interest. "Maybe," he said. "But I wonder what Percy could do with a balanced sword…"

Friday afternoon, I was sitting with Grover at the lake, resting from a near-death experience on the climbing wall. Grover had scampered to the top like a mountain goat, but the lava had almost gotten me. My shirt had smoking holes in it. The hairs had been singed off my forearms.

We sat on the pier, watching the naiads do underwater basket-weaving, until I got up the nerve to ask Grover how his conversation had gone with Mr. D.

His face turned a sickly shade of yellow.

"Fine," he said. "Just great."

"So your career's still on track?"

He glanced at me nervously. "Chiron t-told you I want a searcher's license?"

"Well… no." I had no idea what a searcher's license was, but it didn't seem like the right time to ask. "He just said you had big plans, you know… and that you needed credit for completing a keeper's assignment. So did you get it?"

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?"