The bus pitched down and somebody screamed. Maybe it was me. Now we were heading straight toward the Atlantic Ocean at a thousand miles an hour, the New England coastline off to our right. And it was getting hot in the bus.

Apollo had been thrown somewhere in the back of the bus, but he started climbing up the rows of seats.

"Take the wheel!" Grover begged him.

"No worries," Apollo said. He looked plenty worried. "She just has to learn to—WHOA!"

I saw what he was seeing. Down below us was a little snow-covered New England town. At least, it used to be snow-covered. As I watched, the snow melted off the trees and the roofs and the lawns. The white steeple on a church turned brown and started to smolder. Little plumes of smoke, like birthday candles, were popping up all over the town. Trees and rooftops were catching fire.

"Pull up!" I yelled.

There was a wild light in Thalia's eyes. She yanked back on the wheel, and I held on this time. As we zoomed up, I could see through the back window that the fires in the town were being snuffed out by the sudden blast of cold.

"There!" Apollo pointed. "Long Island, dead ahead. Let's slow down, dear. 'Dead' is only an expression."

Thalia was thundering toward the coastline of northern Long Island. There was Camp Half-Blood: the valley, the woods, the beach. I could see the dining pavilion and cabins and the amphitheater.

"I'm under control," Thalia muttered. "I'm under control."

We were only a few hundred yards away now.

"Brake," Apollo said.

"I can do this."

"BRAKE!"

Thalia slammed her foot on the brake, and the sun bus pitched forward at a forty-five-degree angle, slamming into the Camp Half-Blood canoe lake with a huge FLOOOOOOSH! Steam billowed up, sending several frightened naiads scrambling out of the water with half-woven wicker baskets.

The bus bobbed to the surface, along with a couple of capsized, half-melted canoes.

"Well," said Apollo with a brave smile. "You were right, my dear. You had everything under control! Let's go see if we boiled anyone important, shall we?"

I'd never seen Camp Half-Blood in winter before, and the snow surprised me.

See, the camp has the ultimate magic climate control. Nothing gets inside the borders unless the director, Mr. D, wants it to. I thought it would be warm and sunny, but instead the snow had been allowed to fall lightly. Frost covered the chariot track and the strawberry fields. The cabins were decorated with tiny flickering lights, like Christmas lights, except they seemed to be balls of real fire. More lights glowed in the woods, and weirdest of all, a fire flickered in the attic window of the Big House, where the Oracle dwelt, imprisoned in an old mummified body. I wondered if the spirit of Delphi was roasting marshmallows up there or something.

"Whoa," Nico said as he climbed off the bus. "Is that a climbing wall?"

"Yeah," I said.

"Why is there lava pouring down it?"

"Little extra challenge. Come on. I'll introduce you to Chiron. Zoe, have you met—"

"I know Chiron," Zoe said stiffly. "Tell him we will be in Cabin Eight. Hunters, follow me."

"I'll show you the way," Grover offered.

"We know the way."

"Oh, really, it's no trouble. It's easy to get lost here, if you don't" — he tripped over a canoe and came up still talking—"like my old daddy goat used to say! Come on!"

Zoe rolled her eyes, but I guess she figured there was no getting rid of Grover. The Hunters shouldered their packs and their bows and headed off toward the cabins. As Bianca di Angelo was leaving, she leaned over and whispered something in her brothers ear. She looked at him for an answer, but Nico just scowled and turned away.

"Take care, sweethearts!" Apollo called after the Hunters. He winked at me. "Watch out for those prophecies, Percy. I'll see you soon."

"What do you mean?"

Instead of answering, he hopped back in the bus. "Later, Thalia," he called. "And, uh, be good!"

He gave her a wicked smile, as if he knew something she didn't. Then he closed the doors and revved the engine. I turned aside as the sun chariot took off in a blast of heat. When I looked back, the lake was steaming. A red Maserati soared over the woods, glowing brighter and climbing higher until it disappeared in a ray of sunlight.

Nico was still looking grumpy. I wondered what his sister had told him.

"Who's Chiron?" he asked. "I don't have his figurine."

"Our activities director," I said. "He's… well, you'll see.

"If those Hunter girls don't like him," Nico grumbled, "that's good enough for me. Let's go."

The second thing that surprised me about camp was how empty it was. I mean, I knew most half-bloods only trained during the summer. Just the year-rounders would be here—the ones who didn't have homes to go to, or would get attacked by monsters too much if they left. But there didn't even seem to be many of them, either.

I spotted Charles Beckendorf from the Hephaestus cabin stoking the forge outside the camp armory. The Stoll brothers, Travis and Connor, from the Hermes cabin, were picking the lock on the camp store. A few kids from the Ares cabin were having a snowball fight with the wood nymphs at the edge of the forest. That was about it. Even my old rival from the Ares cabin, Clarisse, didn't seem to be around.

The Big House was decorated with strings of red and yellow fireballs that warmed the porch but didn't seem to catch anything on fire. Inside, flames crackled in the hearth. The air smelled like hot chocolate. Mr. D, the camp director, and Chiron were playing a quiet game of cards in the parlor.

Chiron's brown beard was shaggier for the winter. His curly hair had grown a little longer. He wasn't posing as a teacher this year, so I guess he could afford to be casual. He wore a fuzzy sweater with a hoofprint design on it, and he had a blanket on his lap that almost hid his wheelchair completely.

He smiled when he saw us. "Percy! Thalia! Ah, and this must be—"

"Nico di Angelo," I said. "He and his sister are half-bloods."

Chiron breathed a sigh of relief. "You succeeded, then."

"Well…"

His smile melted. "What's wrong? And where is Annabeth?"

"Oh, dear," Mr. D said in a bored voice, "Not another one lost."

I'd been trying not to pay attention to Mr. D, but he was kind of hard to ignore in his neon orange leopard-skin warm-up suit and his purple running shoes. (Like Mr. D had ever run a day in his immortal life.) A golden laurel wreath was tilted sideways on his curly black hair, which must've meant he'd won the last hand of cards.

"What do you mean?" Thalia asked. "Who else is lost?"

Just then, Grover trotted into the room, grinning like crazy. He had a black eye and red lines on his face that looked like a slap mark. "The Hunters are all moved in!"

Chiron frowned. "The Hunters, eh? I see we have much to talk about." He glanced at Nico. "Grover, perhaps you should take our young friend to the den and show him our orientation film."

"But… Oh, right. Yes, sir."

"Orientation film?" Nico asked. "Is it G or PG? 'Cause Bianca is kinda strict—"

"It's PG-13," Grover said.

"Cool!" Nico happily followed him out of the room.

"Now," Chiron said to Thalia and me, "perhaps you two should sit down and tell us the whole story."

When we were done, Chiron turned to Mr. D. "We should launch a search for Annabeth immediately."

"I'll go," Thalia and I said at the same time.

Mr. D sniffed. "Certainly not!"

Thalia and I both started complaining, but Mr. D held up his hand. He had that purplish angry fire in his eyes that usually meant something bad and godly was going to happen if we didn't shut up.