t didn't take me long to pack. I decided to leave the Minotaur horn in my cabin, which left me only an extra change of clothes and a toothbrush to stuff in a backpack Grover had found for me.

The camp store loaned me one hundred dollars in mortal money and twenty golden drachmas. These coins were as big as Girl Scout cookies and had images of various Greek gods stamped on one side and the EmpireStateBuilding on the other. The ancient mortal drachmas had been silver, Chiron told us, but Olympians never used less than pure gold. Chiron said the coins might come in handy for non-mortal transactions—whatever that meant. He gave Annabeth and me each a canteen of nectar and a Ziploc bag full of ambrosia squares, to be used only in emergencies, if we were seriously hurt. It was god food, Chiron reminded us. It would cure us of almost any injury, but it was lethal to mortals. Too much of it would make a half-blood very, very feverish. An overdose would burn us up, literally.

Annabeth was bringing her magic Yankees cap, which she told me had been a twelfth-birthday present from her mom. She carried a book on famous classical architecture, written in Ancient Greek, to read when she got bored, and a long bronze knife, hidden in her shirt sleeve. I was sure the knife would get us busted the first time we went through a metal detector.

Grover wore his fake feet and his pants to pass as human. He wore a green rasta-style cap, because when it rained his curly hair flattened and you could just see the tips of his horns. His bright orange backpack was full of scrap metal and apples to snack on. In his pocket was a set of reed pipes his daddy goat had carved for him, even though he only knew two songs: Mozart's Piano Concerto no. 12 and Hilary Duff's "So Yesterday," both of which sounded pretty bad on reed pipes.

We waved good-bye to the other campers, took one last look at the strawberry fields, the ocean, and the Big House, then hiked up Half-Blood Hill to the tall pine tree that used to be Thalia, daughter of Zeus.

Chiron was waiting for us in his wheelchair. Next to him stood the surfer dude I'd seen when I was recovering in the sick room. According to Grover, the guy was the camp's head of security. He supposedly had eyes all over his body so he could never be surprised. Today, though, he was wearing a chauffeur's uniform, so I could only see extra peepers on his hands, face and neck.

"This is Argus," Chiron told me. "He will drive you into the city, and, er, well, keep an eye on things."

I heard footsteps behind us.

Luke came running up the hill, carrying a pair of basketball shoes.

"Hey!" he panted. "Glad I caught you."

Annabeth blushed, the way she always did when Luke was around.

"Just wanted to say good luck," Luke told me. "And I thought... um, maybe you could use these."

He handed me the sneakers, which looked pretty normal. They even smelled kind of normal.

Luke said, "Maia!"

White bird's wings sprouted out of the heels, startling me so much, I dropped them. The shoes flapped around on the ground until the wings folded up and disappeared.

"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.

* * *

Argus drove us out of the countryside and into western Long Island. It felt weird to be on a highway again, Annabeth and Grover sitting next to me as if we were normal carpoolers. After two weeks at Half-Blood Hill, the real world seemed like a fantasy. I found myself staring at every McDonald's, every kid in the back of his parents' car, every billboard and shopping mall.

"So far so good," I told Annabeth. "Ten miles and not a single monster."

She gave me an irritated look. "It's bad luck to talk that way, seaweed brain."

"Remind me again—why do you hate me so much?"

"I don't hate you."

"Could've fooled me."

She folded her cap of invisibility. "Look... we're just not supposed to get along, okay? Our parents are rivals."

"Why?"

She sighed. "How many reasons do you want? One time my mom caught Poseidon with his girlfriend in Athena's temple, which is hugely disrespectful. Another time, Athena and Poseidon competed to be the patron god for the city of Athens. Your dad created some stupid saltwater spring for his gift. My mom created the olive tree. The people saw that her gift was better, so they named the city after her."

"They must really like olives."

"Oh, forget it."

"Now, if she'd invented pizza—that I could understand."

"I said, forget it!"

In the front seat, Argus smiled. He didn't say anything, but one blue eye on the back of his neck winked at me.

Traffic slowed us down in Queens. By the time we got into Manhattan it was sunset and starting to rain.

Argus dropped us at the Greyhound Station on the Upper East Side, not far from my mom and Gabe's apartment. Taped to a mailbox was a soggy flyer with my picture on it: HAVE YOU SEEN THIS BOY?

I ripped it down before Annabeth and Grover could notice.

Argus unloaded our bags, made sure we got our bus tickets, then drove away, the eye on the back of his hand opening to watch us as he pulled out of the parking lot.

I thought about how close I was to my old apartment. On a normal day, my mom would be home from the candy store by now. Smelly Gabe was probably up there right now, playing poker, not even missing her.

Grover shouldered his backpack. He gazed down the street in the direction I was looking. "You want to know why she married him, Percy?"

I stared at him. "Were you reading my mind or something?"

"Just your emotions." He shrugged. "Guess I forgot to tell you satyrs can do that. You were thinking about your mom and your stepdad, right?"

I nodded, wondering what else Grover might've forgotten to tell me.

"Your mom married Gabe for you," Grover told me. "You call him 'Smelly,' but you've got no idea. The guy has this aura…. Yuck. I can smell him from here. I can smell traces of him on you, and you haven't been near him for a week."

"Thanks," I said. "Where's the nearest shower?"

"You should be grateful, Percy. Your stepfather smells so repulsively human he could mask the presence of any demigod. As soon as I took a whiff inside his Camaro, I knew: Gabe has been covering your scent for years. If you hadn't lived with him every summer, you probably would've been found by monsters a long time ago. Your mom stayed with him to protect you. She was a smart lady. She must've loved you a lot to put up with that guy—if that makes you feel any better."

It didn't, but I forced myself not to show it. I'll see her again, I thought. She isn't gone.

I wondered if Grover could still read my emotions, mixed up as they were. I was glad he and Annabeth were with me, but I felt guilty that I hadn't been straight with them. I hadn't told them the real reason I'd said yes to this crazy quest.

The truth was, I didn't care about retrieving Zeus's lightning bolt, or saving the world, or even helping my father out of trouble. The more I thought about it, I resented Poseidon for never visiting me, never helping my mom, never even sending a lousy child-support check. He'd only claimed me because he needed a job done.

All I cared about was my mom. Hades had taken her unfairly, and Hades was going to give her back.

You will be betrayed by one who calls you a friend, the Oracle whispered in my mind. You will fail to save what matters most in the end.

Shut up, I told it.

The rain kept coming down.

We got restless waiting for the bus and decided to play some Hacky Sack with one of Grover's apples. Annabeth was unbelievable. She could bounce the apple off her knee, her elbow, her shoulder, whatever. I wasn't too bad myself.

The game ended when I tossed the apple toward Grover and it got too close to his mouth. In one mega goat bite, our Hacky Sack disappeared—core, stem, and all.

Grover blushed. He tried to apologize, but Annabeth and I were too busy cracking up.

Finally the bus came. As we stood in line to board, Grover started looking around, sniffing the air like he smelled his favorite school cafeteria delicacy—enchiladas.

"What is it?" I asked.

"I don't know," he said tensely. "Maybe it's nothing."

But I could tell it wasn't nothing. I started looking over my shoulder, too.

I was relieved when we finally got on board and found seats together in the back of the bus. We stowed our backpacks. Annabeth kept slapping her Yankees cap nervously against her thigh.

As the last passengers got on, Annabeth clamped her hand onto my knee. "Percy."

An old lady had just boarded the bus. She wore a crumpled velvet dress, lace gloves, and a shapeless orange-knit hat that shadowed her face, and she carried a big paisley purse. When she tilted her head up, her black eyes glittered, and my heart skipped a beat.

It was Mrs. Dodds. Older, more withered, but definitely the same evil face.

I scrunched down in my seat.

Behind her came two more old ladies: one in a green hat, one in a purple hat. Otherwise they looked exactly like Mrs. Dodds—same gnarled hands, paisley handbags, wrinkled velvet dresses. Triplet demon grandmothers.

They sat in the front row, right behind the driver. The two on the aisle crossed their legs over the walkway, making an X. It was casual enough, but it sent a clear message: nobody leaves.

The bus pulled out of the station, and we headed through the slick streets of Manhattan. "She didn't stay dead long," I said, trying to keep my voice from quivering. "I thought you said they could be dispelled for a lifetime."

"I said if you're lucky," Annabeth said. "You're obviously not."

"All three of them," Grover whimpered. "Di immortales!"

"It's okay," Annabeth said, obviously thinking hard. "The Furies. The three worst monsters from the Underworld. No problem. No problem. We'll just slip out the windows."

"They don't open," Grover moaned.

"A back exit?" she suggested.

There wasn't one. Even if there had been, it wouldn't have helped. By that time, we were on Ninth Avenue, heading for the Lincoln Tunnel.

"They won't attack us with witnesses around," I said. "Will they?"

"Mortals don't have good eyes," Annabeth reminded me. "Their brains can only process what they see through the Mist."

"They'll see three old ladies killing us, won't they?"

She thought about it. "Hard to say. But we can't count on mortals for help. Maybe an emergency exit in the roof...?"

We hit the Lincoln Tunnel, and the bus went dark except for the running lights down the aisle. It was eerily quiet without the sound of the rain.

Mrs. Dodds got up. In a flat voice, as if she'd rehearsed it, she announced to the whole bus: "I need to use the rest-room."

"So do I," said the second sister.

"So do I," said the third sister.

They all started coming down the aisle.

"I've got it," Annabeth said. "Percy, take my hat."

"What?"

"You're the one they want. Turn invisible and go up the aisle. Let them pass you. Maybe you can get to the front and get away."

"But you guys—"

"There's an outside chance they might not notice us," Annabeth said. "You're a son of one of the Big Three. Your smell might be overpowering."

"I can't just leave you."

"Don't worry about us," Grover said. "Go!"

My hands trembled. I felt like a coward, but I took the Yankees cap and put it on.

When I looked down, my body wasn't there anymore.

I started creeping up the aisle. I managed to get up ten rows, then duck into an empty seat just as the Furies walked past.

Mrs. Dodds stopped, sniffing, and looked straight at me. My heart was pounding.

Apparently she didn't see anything. She and her sisters kept going.

I was free. I made it to the front of the bus. We were almost through the Lincoln Tunnel now. I was about to press the emergency stop button when I heard hideous wailing from the back row.

The old ladies were not old ladies anymore. Their faces were still the same—I guess those couldn't get any uglier— but their bodies had shriveled into leathery brown hag bodies with bat's wings and hands and feet like gargoyle claws. Their handbags had turned into fiery whips.

The Furies surrounded Grover and Annabeth, lashing their whips, hissing: "Where is it? Where?"

The other people on the bus were screaming, cowering in their seats. They saw something, all right.

"He's not here!" Annabeth yelled. "He's gone!"

The Furies raised their whips.

Annabeth drew her bronze knife. Grover grabbed a tin can from his snack bag and prepared to throw it.

What I did next was so impulsive and dangerous I should've been named ADHD poster child of the year.

The bus driver was distracted, trying to see what was going on in his rearview mirror.

Still invisible, I grabbed the wheel from him and jerked it to the left. Everybody howled as they were thrown to the right, and I heard what I hoped was the sound of three Furies smashing against the windows.

"Hey!" the driver yelled. "Hey—whoa!"

We wrestled for the wheel. The bus slammed against the side of the tunnel, grinding metal, throwing sparks a mile behind us.

We careened out of the Lincoln Tunnel and back into the rainstorm, people and monsters tossed around the bus, cars plowed aside like bowling pins.

Somehow the driver found an exit. We shot off the highway, through half a dozen traffic lights, and ended up barreling down one of those New Jersey rural roads where you can't believe there's so much nothing right across the river from New York. There were woods to our left, the Hudson River to our right, and the driver seemed to be veering toward the river.

Another great idea: I hit the emergency brake.

The bus wailed, spun a full circle on the wet asphalt, and crashed into the trees. The emergency lights came on. The door flew open. The bus driver was the first one out, the passengers yelling as they stampeded after him. I stepped into the driver's seat and let them pass.

The Furies regained their balance. They lashed their whips at Annabeth while she waved her knife and yelled in Ancient Greek, telling them to back off. Grover threw tin cans.

I looked at the open doorway. I was free to go, but I couldn't leave my friends. I took off the invisible cap. "Hey!"

The Furies turned, baring their yellow fangs at me, and the exit suddenly seemed like an excellent idea. Mrs. Dodds stalked up the aisle, just as she used to do in class, about to deliver my F- math test. Every time she flicked her whip, red flames danced along the barbed leather.

Her two ugly sisters hopped on top of the seats on either side of her and crawled toward me like huge nasty lizards.

"Perseus Jackson," Mrs. Dodds said, in an accent that was definitely from somewhere farther south than Georgia. "You have offended the gods. You shall die."

"I liked you better as a math teacher," I told her.

She growled.

Annabeth and Grover moved up behind the Furies cautiously, looking for an opening.

I took the ballpoint pen out of my pocket and uncapped it. Riptide elongated into a shimmering double-edged sword.

The Furies hesitated.

Mrs. Dodds had felt Riptide's blade before. She obviously didn't like seeing it again.

"Submit now," she hissed. "And you will not suffer eternal torment."

"Nice try," I told her.

"Percy, look out!" Annabeth cried.

Mrs. Dodds lashed her whip around my sword hand while the Furies on the either side lunged at me.

My hand felt like it was wrapped in molten lead, but I managed not to drop Riptide. I stuck the Fury on the left with its hilt, sending her toppling backward into a seat. I turned and sliced the Fury on the right. As soon as the blade connected with her neck, she screamed and exploded into dust. Annabeth got Mrs. Dodds in a wrestler's hold and yanked her backward while Grover ripped the whip out of her hands.

"Ow!" he yelled. "Ow! Hot! Hot!"

The Fury I'd hilt-slammed came at me again, talons ready, but I swung Riptide and she broke open like a piñata.

Mrs. Dodds was trying to get Annabeth off her back. She kicked, clawed, hissed and bit, but Annabeth held on while Grover got Mrs. Dodds's legs tied up in her own whip. Finally they both shoved her backward into the aisle. Mrs. Dodds tried to get up, but she didn't have room to flap her bat wings, so she kept falling down.

"Zeus will destroy you!" she promised. "Hades will have your soul!"

"Braccas meas vescimini!" I yelled.

I wasn't sure where the Latin came from. I think it meant "Eat my pants!"

Thunder shook the bus. The hair rose on the back of my neck.

"Get out!" Annabeth yelled at me. "Now!" I didn't need any encouragement.

We rushed outside and found the other passengers wandering around in a daze, arguing with the driver, or running around in circles yelling, "We're going to die!" A Hawaiian-shirted tourist with a camera snapped my photograph before I could recap my sword.

"Our bags!" Grover realized. "We left our—"

BOOOOOM!

The windows of the bus exploded as the passengers ran for cover. Lightning shredded a huge crater in the roof, but an angry wail from inside told me Mrs. Dodds was not yet dead.

"Run!" Annabeth said. "She's calling for reinforcements! We have to get out of here!"

We plunged into the woods as the rain poured down, the bus in flames behind us, and nothing but darkness ahead.