"Awesome!" Grover said.

Luke smiled. "Those served me well when I was on my quest. Gift from Dad. Of course, I don't use them much these days…." His expression turned sad.

I didn't know what to say. It was cool enough that Luke had come to say good-bye. I'd been afraid he might resent me for getting so much attention the last few days. But here he was giving me a magic gift…. It made me blush almost as much as Annabeth.

"Hey, man," I said. "Thanks."

"Listen, Percy…" Luke looked uncomfortable. "A lot of hopes are riding on you. So just… kill some monsters for me, okay?"

We shook hands. Luke patted Grover's head between his horns, then gave a good-bye hug to Annabeth, who looked like she might pass out.

After Luke was gone, I told her, "You're hyperventilating."

"Am not."

"You let him capture the flag instead of you, didn't you?"

"Oh… why do I want to go anywhere with you, Percy?"

She stomped down the other side of the hill, where a white SUV waited on the shoulder of the road. Argus followed, jingling his car keys.

I picked up the flying shoes and had a sudden bad feeling. I looked at Chiron. "I won't be able to use these, will I?"

He shook his head. "Luke meant well, Percy. But taking to the air… that would not be wise for you."

I nodded, disappointed, but then I got an idea. "Hey, Grover. You want a magic item?"

His eyes lit up. "Me?"

Pretty soon we'd laced the sneakers over his fake feet, and the world's first flying goat boy was ready for launch.

"Maia!" he shouted.

He got off the ground okay, but then fell over sideways so his backpack dragged through the grass. The winged shoes kept bucking up and down like tiny broncos.

"Practice," Chiron called after him. "You just need practice!"

"Aaaaa!" Grover went flying sideways down the hill like a possessed lawn mower, heading toward the van.

Before I could follow, Chiron caught my arm. "I should have trained you better, Percy," he said. "If only I had more time. Hercules, Jason—they all got more training."

"That's okay. I just wish—"

I stopped myself because I was about to sound like a brat. I was wishing my dad had given me a cool magic item to help on the quest, something as good as Luke's flying shoes, or Annabeth's invisible cap.

"What am I thinking?" Chiron cried. "I can't let you get away without this."

He pulled a pen from his coat pocket and handed it to me. It was an ordinary disposable ballpoint, black ink, removable cap. Probably cost thirty cents.

"Gee," I said. "Thanks."

"Percy, that's a gift from your father. I've kept it for years, not knowing you were who I was waiting for. But the prophecy is clear to me now. You are the one."

I remembered the field trip to the Metropolitan Museum of Art, when I'd vaporized Mrs. Dodds. Chiron had thrown me a pen that turned into a sword. Could this be…?

I took off the cap, and the pen grew longer and heavier in my hand. In half a second, I held a shimmering bronze sword with a double-edged blade, a leather-wrapped grip, and a flat hilt riveted with gold studs. It was the first weapon that actually felt balanced in my hand.

"The sword has a long and tragic history that we need not go into," Chiron told me. "Its name is Anaklusmos."

"'Riptide, " I translated, surprised the Ancient Greek came so easily.

"Use it only for emergencies," Chiron said, "and only against monsters. No hero should harm mortals unless absolutely necessary, of course, but this sword wouldn't harm them in any case."

I looked at the wickedly sharp blade. "What do you mean it wouldn't harm mortals? How could it not?"

"The sword is celestial bronze. Forged by the Cyclopes, tempered in the heart of Mount Etna, cooled in the River Lethe. It's deadly to monsters, to any creature from the Underworld, provided they don't kill you first. But the blade will pass through mortals like an illusion. They simply are not important enough for the blade to kill. And I should warn you: as a demigod, you can be killed by either celestial or normal weapons. You are twice as vulnerable."

"Good to know."

"Now recap the pen."

I touched the pen cap to the sword tip and instantly Riptide shrank to a ballpoint pen again. I tucked it in my pocket, a little nervous, because I was famous for losing pens at school.

"You can't," Chiron said.

"Can't what?"

"Lose the pen," he said. "It is enchanted. It will always reappear in your pocket. Try it."

I was wary, but I threw the pen as far as I could down the hill and watched it disappear in the grass.

"It may take a few moments," Chiron told me. "Now check your pocket."

Sure enough, the pen was there.

"Okay, that's extremely cool," I admitted. "But what if a mortal sees me pulling out a sword?"

Chiron smiled. "Mist is a powerful thing, Percy."

"Mist?"

"Yes. Read The Iliad. It's full of references to the stuff. Whenever divine or monstrous elements mix with the mortal world, they generate Mist, which obscures the vision of humans. You will see things just as they are, being a half-blood, but humans will interpret things quite differently. Remarkable, really, the lengths to which humans will go to fit things into their version of reality."

I put Riptide back in my pocket.

For the first time, the quest felt real. I was actually leaving Half-Blood Hill. I was heading west with no adult supervision, no backup plan, not even a cell phone. (Chiron said cell phones were traceable by monsters; if we used one, it would be worse than sending up a flare.) I had no weapon stronger than a sword to fight off monsters and reach the Land of the Dead.

"Chiron…" I said. "When you say the gods are immortal… I mean, there was a time before them, right?"

"Four ages before them, actually. The Time of the Titans was the Fourth Age, sometimes called the Golden Age, which is definitely a misnomer. This, the time of Western civilization and the rule of Zeus, is the Fifth Age."

"So what was it like… before the gods?"

Chiron pursed his lips. "Even I am not old enough to remember that, child, but I know it was a time of darkness and savagery for mortals. Kronos, the lord of the Titans, called his reign the Golden Age because men lived innocent and free of all knowledge. But that was mere propaganda. The Titan king cared nothing for your kind except as appetizers or a source of cheap entertainment. It was only in the early reign of Lord Zeus, when Prometheus the good Titan brought fire to mankind, that your species began to progress, and even then Prometheus was branded a radical thinker. Zeus punished him severely, as you may recall. Of course, eventually the gods warmed to humans, and Western civilization was born."

"But the gods can't die now, right? I mean, as long as Western civilization is alive, they're alive. So… even if I failed, nothing could happen so bad it would mess up everything, right?"

Chiron gave me a melancholy smile. "No one knows how long the Age of the West will last, Percy. The gods are immortal, yes. But then, so were the Titans. They still exist, locked away in their various prisons, forced to endure endless pain and punishment, reduced in power, but still very much alive. May the Fates forbid that the gods should ever suffer such a doom, or that we should ever return to the darkness and chaos of the past. All we can do, child, is follow our destiny."

"Our destiny… assuming we know what that is."

"Relax," Chiron told me. "Keep a clear head. And remember, you may be about to prevent the biggest war in human history."

"Relax," I said. "I'm very relaxed."

When I got to the bottom of the hill, I looked back. Under the pine tree that used to be Thalia, daughter of Zeus, Chiron was now standing in full horse-man form, holding his bow high in salute. Just your typical summer-camp send-off by your typical centaur.