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."