was staring at the waves when Annabeth and Tyson found me.

“What’s going on?” Annabeth asked. “I heard you calling for help!”

“Me, too!” Tyson said. “Heard you yell, ‘Bad things are attacking!’”

“I didn’t call you guys,” I said. “I’m fine.”

“But then who …” Annabeth noticed the three yellow duffel bags, then the thermos and the bottle of vitamins I was holding. “What—”

“Just listen,” I said. “We don’t have much time.”

I told them about my conversation with Hermes. By the time I was finished, I could hear screeching in the distance—patrol harpies picking up our scent.

“Percy,” Annabeth said, “we have to do the quest.”

“We’ll get expelled, you know. Trust me, I’m an expert at getting expelled.”

“So? If we fail, there won’t be any camp to come back to.”

“Yeah, but you promised Chiron—”

“I promised I’d keep you from danger. I can only do that by coming with you! Tyson can stay behind and tell them—”

“I want to go,” Tyson said.

“No!” Annabeth’s voice sounded close to panic. “I mean … Percy, come on. You know that’s impossible.”

I wondered again why she had such a grudge against Cyclopes. There was something she wasn’t telling me.

She and Tyson both looked at me, waiting for an answer. Meanwhile, the cruise ship was getting farther and farther away.

The thing was, part of me didn’t want Tyson along. I’d spent the last three days in close quarters with the guy, getting razzed by the other campers and embarrassed a million times a day, constantly reminded that I was related to him. I needed some space.

Plus, I didn’t know how much help he’d be, or how I’d keep him safe. Sure, he was strong, but Tyson was a little kid in Cyclops terms, maybe seven or eight years old, mentally. I could see him freaking out and starting to cry while we were trying to sneak past a monster or something. He’d get us all killed.

On the other hand, the sound of the harpies was getting closer….

“We can’t leave him,” I decided. “Tantalus will punish him for us being gone.”

“Percy,” Annabeth said, trying to keep her cool, “we’re going to Polyphemus’s island!

Polyphemus is an S-i-k … a C-y-k…” She stamped her foot in frustration. As smart as she was, Annabeth was dyslexic, too. We could’ve been there all night while she tried to spell Cyclops. “You know what I mean!”

“Tyson can go,” I insisted, “if he wants to.”

Tyson clapped his hands. “Want to!”

Annabeth gave me the evil eye, but I guess she could tell I wasn’t going to change my mind.

Or maybe she just knew we didn’t have time to argue.

“All right,” she said. “How do we get to that ship?”

“Hermes said my father would help.”

“Well then, Seaweed Brain? What are you waiting for?”

I’d always had a hard time calling on my father, or praying, or whatever you want to call it, but I stepped into the waves.

“Urn, Dad?” I called. “How’s it going?”

“Percy!” Annabeth whispered. “We’re in a hurry!”

“We need your help,” I called a little louder. “We need to get to that ship, like, before we get eaten and stuff, so …”

At first, nothing happened. Waves crashed against the shore like normal. The harpies sounded like they were right behind the sand dunes. Then, about a hundred yards out to sea, three white lines appeared on the surface. They moved fast toward the shore, like claws ripping through the ocean.

As they neared the beach, the surf burst apart and the heads of three white stallions reared out of the waves.

Tyson caught his breath. “Fish ponies!”

He was right. As the creatures pulled themselves onto the sand, I saw that they were only horses in the front; their back halves were silvery fish bodies, with glistening scales and rainbow tail fins.

“Hippocampi!” Annabeth said. “They’re beautiful.”

The nearest one whinnied in appreciation and nuzzled Annabeth.

“We’ll admire them later,” I said. “Come on!”

“There!” a voice screeched behind us. “Bad children out of cabins! Snack time for lucky harpies!”

Five of them were fluttering over the top of the dunes—plump little hags with pinched faces and talons and feathery wings too small for their bodies. They reminded me of miniature cafeteria ladies who’d been crossbred with dodo birds. They weren’t very fast, thank the gods, but they were vicious if they caught you.

“Tyson!” I said. “Grab a duffel bag!”

He was still staring at the hippocampi with his mouth hanging open, “Tyson!”

“Uh?”

“Come on!”

With Annabeth’s help I got him moving. We gathered the bags and mounted our steeds.

Poseidon must’ve known Tyson was one of the passengers, because one hippocampus was much larger than the other two—just right for carrying a Cyclops.

“Giddyup!” I said. My hippocampus turned and plunged into the waves. Annabeth’s and Tyson’s followed right behind.

The harpies cursed at us, wailing for their snacks to come back, but the hippocampi raced over the water at the speed of Jet Skis. The harpies fell behind, and soon the shore of Camp Half-Blood was nothing but a dark smudge. I wondered if I’d ever see the place again. But right then I had other problems.

The cruise ship was now looming in front of us—our ride toward Florida and the Sea of Monsters.

Riding the hippocampus was even easier than riding a pegasus. We zipped along with the wind in our faces, speeding through the waves so smooth and steady I hardly needed to hold on at all.

As we got closer to the cruise ship, I realized just how huge it was. I felt as though I were looking up at a building in Manhattan. The white hull was at least ten stories tall, topped with another dozen levels of decks with brightly lit balconies and portholes. The ship’s name was painted just above the bow line in black letters, lit with a spotlight. It took me a few seconds to decipher it:

PRINCESS ANDROMEDA

Attached to the bow was a huge masthead—a three-story-tall woman wearing a white Greek chiton, sculpted to look as if she were chained to the front of the ship. She was young and beautiful, with flowing black hair, but her expression was one of absolute terror. Why anybody would want a screaming princess on the front of their vacation ship, I had no idea.

I remembered the myth about Andromeda and how she had been chained to a rock by her own parents as a sacrifice to a sea monster. Maybe she’d gotten too many F’s on her report card or something. Anyway, my namesake, Perseus, had saved her just in time and turned the sea monster to stone using the head of Medusa.

That Perseus always won. That’s why my mom had named me after him, even though he was a son of Zeus and I was a son of Poseidon. The original Perseus was one of the only heroes in the Greek myths who got a happy ending. The others died—betrayed, mauled, mutilated, poisoned, or cursed by the gods. My mom hoped I would inherit Perseus’s luck. Judging by how my life was going so far, I wasn’t real optimistic.

“How do we get aboard?” Annabeth shouted over the noise of the waves, but the hippocampi seemed to know what we needed. They skimmed along the starboard side of the ship, riding easily through its huge wake, and pulled up next to a service ladder riveted to the side of the hull.

“You first,” I told Annabeth.

She slung her duffel bag over her shoulder and grabbed the bottom rung. Once she’d hoisted herself onto the ladder, her hippocampus whinnied a farewell and dove underwater.

Annabeth began to climb. I let her get a few rungs up, then followed her.

Finally it was just Tyson in the water. His hippocampus was treating him to 360° aerials and backward ollies, and Tyson was laughing so hysterically, the sound echoed up the side of the ship.

“Tyson, shhh!” I said. “Come on, big guy!”

“Can’t we take Rainbow?” he asked, his smile fading.

I stared at him. “Rainbow?”

The hippocampus whinnied as if he liked his new name.

“Um, we have to go,” I said. “Rainbow … well, he can’t climb ladders.”

Tyson sniffled. He buried his face in the hippocampus’s mane. “I will miss you, Rainbow!”

The hippocampus made a neighing sound I could’ve sworn was crying.

“Maybe we’ll see him again sometime,” I suggested.

“Oh, please!” Tyson said, perking up immediately. “Tomorrow!”

I didn’t make any promises, but I finally convinced Tyson to say his farewells and grab hold of the ladder. With a final sad whinny, Rainbow the hippocampus did a back-flip and dove into the sea.

The ladder led to a maintenance deck stacked with yellow lifeboats. There was a set of locked double doors, which Annabeth managed to pry open with her knife and a fair amount of cursing in Ancient Greek.

I figured we’d have to sneak around, being stowaways and all, but after checking a few corridors and peering over a balcony into a huge central promenade lined with closed shops, I began to realize there was nobody to hide from. I mean, sure it was the middle of the night, but we walked half the length of the boat and met no one. We passed forty or fifty cabin doors and heard no sound behind any of them.

“It’s a ghost ship,” I murmured.

“No,” Tyson said, fiddling with the strap of his duffel bag. “Bad smell.”

Annabeth frowned. “I don’t smell anything.”

“Cyclopes are like satyrs,” I said. “They can smell monsters. Isn’t that right, Tyson?”

He nodded nervously. Now that we were away from Camp Half-Blood, the Mist had distorted his face again. Unless I concentrated very hard, it seemed that he had two eyes instead of one.

“Okay,” Annabeth said. “So what exactly do you smell?”

“Something bad,” Tyson answered.

“Great,” Annabeth grumbled. “That clears it up.”

We came outside on the swimming pool level. There were rows of empty deck chairs and a bar closed off with a chain curtain. The water in the pool glowed eerily, sloshing back and forth from the motion of the ship.

Above us fore and aft were more levels—a climbing wall, a putt-putt golf course, a revolving restaurant, but no sign of life.

And yet … I sensed something familiar. Something dangerous. I had the feeling that if I weren’t so tired and burned out on adrenaline from our long night, I might be able to put a name to what was wrong.

“We need a hiding place,” I said. “Somewhere safe to sleep.”

“Sleep,” Annabeth agreed wearily.

We explored a few more corridors until we found an empty suite on the ninth level. The door was open, which struck me as weird. There was a basket of chocolate goodies on the table, an iced-down bottle of sparkling cider on the nightstand, and a mint on the pillow with a handwritten note that said: Enjoy your cruise!

We opened our duffel bags for the first time and found that Hermes really had thought of everything—extra clothes, toiletries, camp rations, a Ziploc bag full of cash, a leather pouch full of golden drachmas. He’d even managed to pack Tyson’s oilcloth with his tools and metal bits, and Annabeth’s cap of invisibility, which made them both feel a lot better.

“I’ll be next door,” Annabeth said. “You guys don’t drink or eat anything.”

“You think this place is enchanted?”

She frowned. “I don’t know. Something isn’t right. Just … be careful.”

We locked our doors.

Tyson crashed on the couch. He tinkered for a few minutes on his metalworking project—which he still wouldn’t show me—but soon enough he was yawning. He wrapped up his oilcloth and passed out.

I lay on the bed and stared out the porthole. I thought I heard voices out in the hallway, like whispering. I knew that couldn’t be. We’d walked all over the ship and had seen nobody. But the voices kept me awake. They reminded me of my trip to the Underworld—the way the spirits of the dead sounded as they drifted past.

Finally my weariness got the best of me. I fell asleep … and had my worst dream yet.

I was standing in a cavern at the edge of an enormous pit. I knew the place too well. The entrance to Tartarus. And I recognized the cold laugh that echoed from the darkness below.

If it isn’t the young hero. The voice was like a knife blade scraping across stone. On his way to another great victory.

I wanted to shout at Kronos to leave me alone. I wanted to draw Riptide and strike him down. But I couldn’t move. And even if I could, how could I kill something that had already been destroyed—chopped to pieces and cast into eternal darkness?

Don’t let me stop you, the titan said. Perhaps this time, when you fail, you’ll wonder if it’s worthwhile slaving for the gods. How exactly has your father shown his appreciation lately?

His laughter filled the cavern, and suddenly the scene changed.

It was a different cave—Grover’s bedroom prison in the Cyclops’s lair.

Grover was sitting at the loom in his soiled wedding dress, madly unraveling the threads of the unfinished bridal train.

“Honeypie!” the monster shouted from behind the boulder.

Grover yelped and began weaving the threads back together.

The room shook as the boulder was pushed aside. Looming in the doorway was a Cyclops so huge he made Tyson look vertically challenged. He had jagged yellow teeth and gnarled hands as big as my whole body. He wore a faded purple T-shirt that said WORLD SHEEP EXPO 2001. He must’ve been at least fifteen feet tall, but the most startling thing was his enormous milky eye, scarred and webbed with cataracts. If he wasn’t completely blind, he had to be pretty darn close.

“What are you doing?” the monster demanded.

“Nothing!” Grover said in his falsetto voice. “Just weaving my bridal train, as you can see.”

The Cyclops stuck one hand into the room and groped around until he found the loom. He pawed at the cloth. “It hasn’t gotten any longer!”

“Oh, um, yes it has, dearest. See? I’ve added at least an inch.”

“Too many delays!” the monster bellowed. Then he sniffed the air. “You smell good! Like goats!”

“Oh.” Grover forced a weak giggle. “Do you like it? It’s Eau de Chevre. I wore it just for you.”

“Mmmm!” The Cyclops bared his pointed teeth. “Good enough to eat!”

“Oh, you’re such a flirt!”

“No more delays!”

“But dear, I’m not done!”

“Tomorrow!”

“No, no. Ten more days.”

“Five!”

“Oh, well, seven then. If you insist.”

“Seven! That is less than five, right?”

“Certainly. Oh yes.”

The monster grumbled, still not happy with his deal, but he left Grover to his weaving and rolled the boulder back into place.

Grover closed his eyes and took a shaky breath, trying to calm his nerves.

“Hurry, Percy,” he muttered. “Please, please, please!”

I woke to a ship’s whistle and a voice on the intercom— some guy with an Australian accent who sounded way too happy.

“Good morning, passengers! We’ll be at sea all day today. Excellent weather for the poolside mambo party! Don’t forget million-dollar bingo in the Kraken Lounge at one o’clock, and for our special guests, disemboweling practice on the Promenade!”

I sat up in bed. “What did he say?”

Tyson groaned, still half asleep. He was lying facedown on the couch, his feet so far over the edge they were in the bathroom. “The happy man said … bowling practice?”

I hoped he was right, but then there was an urgent knock on the suite’s interior door.

Annabeth stuck her head in—her blond hair in a rat’s nest. “Disemboweling practice?”

Once we were all dressed, we ventured out into the ship and were surprised to see other people. A dozen senior citizens were heading to breakfast. A dad was taking his kids to the pool for a morning swim. Crew members in crisp white uniforms strolled the deck, tipping their hats to the passengers.

Nobody asked who we were. Nobody paid us much attention. But there was something wrong.

As the family of swimmers passed us, the dad told his kids: “We are on a cruise. We are having fun.”

“Yes,” his three kids said in unison, their expressions blank. “We are having a blast. We will swim in the pool.”

They wandered off.

“Good morning,” a crew member told us, his eyes glazed. “We are all enjoying ourselves aboard the Princess Andromeda. Have a nice day.” He drifted away.

“Percy, this is weird,” Annabeth whispered. “They’re all in some kind of trance.”

Then we passed a cafeteria and saw our first monster. It was a hellhound—a black mastiff with its front paws up on the buffet line and its muzzle buried in the scrambled eggs. It must’ve been young, because it was small compared to most—no bigger than a grizzly bear. Still, my blood turned cold. I’d almost gotten killed by one of those before.

The weird thing was: a middle-aged couple was standing in the buffet line right behind the devil dog, patiently waiting their turn for the eggs. They didn’t seem to notice anything out of the ordinary.

“Not hungry anymore,” Tyson murmured.

Before Annabeth or I could reply, a reptilian voice came from down the corridor, “Ssssix more joined yesssterday.”

Annabeth gestured frantically toward the nearest hiding place—the women’s room—and all three of us ducked inside. I was so freaked out it didn’t even occur to me to be embarrassed.

Something—or more like two somethings—slithered past the bathroom door, making sounds like sandpaper against the carpet.

“Yesss,” a second reptilian voice said. “He drawssss them. Ssssoon we will be sssstrong.”

The things slithered into the cafeteria with a cold hissing that might have been snake laughter.

Annabeth looked at me. “We have to get out of here.”

“You think I want to be in the girls’ restroom?”

“I mean the ship, Percy! We have to get off the ship.”

“Smells bad,” Tyson agreed. “And dogs eat all the eggs. Annabeth is right. We must leave the restroom and ship.”

I shuddered. If Annabeth and Tyson were actually agreeing about something, I figured I’d better listen.

Then I heard another voice outside—one that chilled me worse than any monster’s.

“—only a matter of time. Don’t push me, Agrius!”

It was Luke, beyond a doubt. I could never forget his voice.

“I’m not pushing you!” another guy growled. His voice was deeper and even angrier than Luke’s. “I’m just saying, if this gamble doesn’t pay off—”

“It’ll pay off,” Luke snapped. “They’ll take the bait. Now, come, we’ve got to get to the admiralty suite and check on the casket.”

Their voices receded down the corridor.

Tyson whimpered. “Leave now?”

Annabeth and I exchanged looks and came to a silent agreement.

“We can’t,” I told Tyson.

“We have to find out what Luke is up to,” Annabeth agreed. “And if possible, we’re going to beat him up, bind him in chains, and drag him to Mount Olympus.”