I heard an explosion in the distance. About half a mile away, a mountain of coral disintegrated under the weight of two giant creatures. I could dimly make out their shapes. One was a lobster. The other was a giant humanoid like a Cyclops, but he was surrounded by a flurry of limbs. At first I thought he wearing a bunch of giant octopi. Then I realized they were his own arms—a hundred flailing, fighting arms.

"Briares!" I said.

I was happy to see him, but he looked like he was fighting for his life. He was the last of his kind—a Hundred-Handed One, cousin of the Cyclopes. We'd saved him from Kronos's prison last summer, and I knew he'd come to help Poseidon, but I hadn't heard of him since.

"He fights well," Poseidon said. "I wish we had a whole army like him, but he is the only one."

I watched as Briares bellowed in rage and picked up the lobster, which thrashed and snapped its pincers. He threw it off the coral mountain, and the lobster disappeared into the darkness. Briares swam after it, his hundred arms spinning like the blades of a motorboat.

"Percy, we may not have much time," my dad said. "Tell me of your mission. Did you see Kronos?"

I told him everything, though my voice choked up when I explained about Beckendorf. I looked down at the courtyards below and saw hundreds of wounded mermen lying on makeshift cots. I saw rows of coral mounds that must've been hastily made graves. I realized Beckendorf wasn't the first death. He was only one of hundreds, maybe thousands. I'd never felt so angry and helpless.

Poseidon stroked his beard. "Percy, Beckendorf chose a heroic death. You bear no blame for that. Kronos's army will be in disarray. Many were destroyed."

"But we didn't kill him, did we?"

As I said it, I knew it was a naive hope. We might blow up his ship and disintegrate his monsters, but a Titan lord wouldn't be so easy to kill.

"No," Poseidon admitted. "But you've bought our side some time."

"There were demigods on that ship," I said, thinking of the kid I'd seen in the stairwell. Somehow I'd allowed myself to concentrate on the monsters and Kronos. I'd convinced myself that destroying their ship was all right because they were evil, they were sailing to attack my city, and besides, they couldn't really be permanently killed. Monsters just vaporized and re-formed eventually. But demigods . . .

Poseidon put his hand on my shoulder. "Percy, there were only a few demigod warriors aboard that ship, and they all chose to battle for Kronos. Perhaps some heeded your warning and escaped. If they did not . . . they chose their path."

"They were brainwashed!" I said. "Now they're dead and Kronos is still alive. That's supposed to make me feel better?"

I glared at the mosaic—little tile explosions destroying tile monsters. It seemed so easy when it was just a picture.

Tyson put his arm around me. If anybody else had tried that, I would've pushed him away, but Tyson was too big and stubborn. He hugged me whether I wanted it or not. "Not your fault, brother. Kronos does not explode good. Next time we will use a big stick."

"Percy," my father said. "Beckendorf's sacrifice wasn't in vain. You have scattered the invasion force. New York will be safe for a time, which frees the other Olympians to deal with the bigger threat."

"The bigger threat?" I thought about what the golden Titan had said in my dream: The gods have answered the challenge. Soon they will be destroyed.

A shadow passed over my father's face. "You've had enough sorrow for one day. Ask Chiron when you return to camp."

"Return to camp? But you're in trouble here. I want to help!"

"You can't, Percy. Your job is elsewhere."

I couldn't believe I was hearing this. I looked at Tyson for backup.

My brother chewed his lip. "Daddy . . . Percy can fight with a sword. He is good."

"I know that," Poseidon said gently.

"Dad, I can help," I said. "I know I can. You're not going to hold out here much longer."

A fireball launched into the sky from behind the enemy lines. I thought Poseidon would deflect it or something, but it landed on the outer corner of the yard and exploded, sending mermen tumbling through the water. Poseidon winced as if he'd just been stabbed.

"Return to camp," he insisted. "And tell Chiron it is time."

"For what?"

"You must hear the prophecy. The entire prophecy."

I didn't need to ask him which prophecy. I'd been hearing about the "Great Prophecy" for years, but nobody would ever tell me the whole thing. All I knew was that I was supposed to make a decision that would decide the fate of the world—but no pressure.

"What if this is the decision?" I said. "Staying here to light, or leaving? What if I leave and you . . ."

I couldn't say die. Gods weren't supposed to die, but I'd seen it happen. Even if they didn't die, they could be reduced to nearly nothing, exiled, imprisoned in the depths of Tartarus like Kronos had been.

"Percy, you must go," Poseidon insisted. "I don't know what your final decision will be, but your fight lies in the world above. If nothing else, you must warn your friends at camp. Kronos knew your plans. You have a spy. We will hold here. We have no choice."

Tyson gripped my hand desperately. "I will miss you, brother!"

Watching us, our father seemed to age another ten years. "Tyson, you have work to do as well, my son. They need you in the armory."

Tyson pouted some more.

"I will go," he sniffled. He hugged me so hard he almost cracked my ribs. "Percy, be careful! Do not let monsters kill you dead!"

I tried to nod confidently, but it was too much for the big guy. He sobbed and swam away toward the armory, where his cousins were fixing spears and swords.

"You should let him fight," I told my father. "He hates being stuck in the armory. Can't you tell?"

Poseidon shook his head. "It is bad enough I must send you into danger. Tyson is too young. I must protect him."

"You should trust him," I said. "Not try to protect him."

Poseidon's eyes flared. I thought I'd gone too far, but then he looked down at the mosaic and his shoulders sagged. On the tiles, the mermaid guy in the crawfish chariot was coming closer to the palace.

"Oceanus approaches," my father said. "I must meet him in battle."

I'd never been scared for a god before, but I didn't see how my dad could face this Titan and win.

"I will hold," Poseidon promised. "I will not give up my domain. Just tell me, Percy, do you still have the birthday gift I gave you last summer?"

I nodded and pulled out my camp necklace. It had a bead for every summer I'd been at Camp Half-Blood, but since last year I'd also kept a sand dollar on the cord. My father had given it to me for my fifteenth birthday. He'd told me I would know when to "spend it," but so far I hadn't figured out what he meant. All I knew was that it didn't fit the vending machines in the school cafeteria.

"The time is coming," he promised. "With luck, I will see you for your birthday next week, and we will have a proper celebration."

He smiled, and for a moment I saw the old light in his eyes.

Then the entire sea grew dark in front of us, like an inky storm was rolling in. Thunder crackled, which should've been impossible underwater. A huge icy presence was approaching. I sensed a wave of fear roll through the armies below us.

"I must assume my true godly form," Poseidon said. "Go—and good luck, my son."

I wanted to encourage him, to hug him or something, but knew better than to stick around. When a god assumes his true form, the power is so great that any mortal looking on him will disintegrate.

"Good-bye, Father," I managed.

Then I turned away. I willed the ocean currents to aid me. Water swirled around me, and I shot toward the surface at speeds that would've caused any normal human to pop like a balloon.

When I looked back, all I could see were flashes of green and blue as my father fought the Titan, and the sea itself was torn apart by the two armies.

THREE

I GET A SNEAK PEEK AT

MY DEATH

If you want to be popular at Camp Half-Blood, don't come back from a mission with bad news.

Word of my arrival spread as soon as I walked out of the ocean. Our beach is on the North Shore of Long Island, and it's enchanted so most people can't even see it. People don't just appear on the beach unless they're demigods or gods or really, really lost pizza delivery guys. (It's happened—but that's another story.)

Anyway, that afternoon the lookout on duty was Connor Stoll from the Hermes cabin. When he spotted me, he got so excited he fell out of his tree. Then he blew the conch horn to signal the camp and ran to greet me.

Connor had a crooked smile that matched his crooked sense of humor. He's a pretty nice guy, but you should always keep one hand on your wallet when he's around, and do not, under any circumstances, give him access to shaving cream unless you want to find your sleeping bag full of it. He's got curly brown hair and is a little shorter than his brother, Travis, which is the only way I can tell them apart. They are both so unlike my old enemy Luke it's hard to believe they're all sons of Hermes.

"Percy!" he yelled. "What happened? Where's Beckendorf?"

Then he saw my expression, and his smile melted. "Oh, no. Poor Silena. Holy Zeus, when she finds out . . ."

Together we climbed the sand dunes. A few hundred yards away, people were already streaming toward us, smiling and excited. Percy's back, they were probably thinking. He's saved the day! Maybe he brought souvenirs!

I stopped at the dining pavilion and waited for them. No sense rushing down there to tell them what a loser I was.

I gazed across the valley and tried to remember how Camp Half-Blood looked the first time I ever saw it. That seemed like a bajillion years ago.

From the dining pavilion, you could see pretty much everything. Hills ringed the valley. On the tallest, Half-Blood Hill, Thalia's pine tree stood with the Golden Fleece hanging from its branches, magically protecting the camp from its enemies. The guard dragon Peleus was so big now I could see him from here—curled around the tree trunk, lending up smoke signals as he snored.

To my right spread the woods. To my left, the canoe lake glittered and the climbing wall glowed from the lava pouring down its side. Twelve cabins—one for each Olympian god—made a horseshoe pattern around the commons area. Farther south were the strawberry fields, the armory, and the four-story Big House with its sky blue paint job and its bronze eagle weathervane.

In some ways, the camp hadn't changed. But you couldn't see the war by looking at the buildings or the fields. You could see it in the faces of the demigods and satyrs and naiads coming up the hill.

There weren't as many at camp as four summers ago. Some had left and never come back. Some had died fighting. Others—we tried not to talk about them—had gone over to the enemy.

The ones who were still here were battle-hardened and weary. There was little laughter at camp these days. Even the Hermes cabin didn't play so many pranks. It's hard to enjoy practical jokes when your whole life feels like one.

Chiron galloped into the pavilion first, which was easy for him since he's a white stallion from the waist down. His beard had grown wilder over the summer. He wore a green T-shirt that said MY OTHER CAR IS A CENTAUR and a bow slung over his back.