Ever come home and found your room messed up? Like some helpful person (hi, Malcolm please don't clean my space again it may look messy but I know where everything is) has tried to 'clean' it, and suddenly you can't find anything? And even if nothing is missing, you get that creepy feeling like somebody's been looking through your private stuff and dusting everything with lemon furniture polish?

That's kind of the way I felt seeing Camp Half-Blood again.

On the surface, things didn't look all that different. The Big House was still there with its blue gabled roof and its wraparound porch. The strawberry fields still baked in the sun. The same whitecolumned Greek buildings were scattered around the valley – the amphitheatre, the combat arena, the dining pavilion overlooking Long Island Sound. And nestled between the woods and the creek were the same cabins – a crazy assortment of twelve buildings, each representing a different Olympian god.

But there was an air of danger now. You could tell something was wrong. Instead of playing volleyball in the sandpit, counsellors and satyrs were stockpiling weapons in the tool shed. Dryads armed with bows and arrows talked nervously at the edge of the woods. The forest looked sickly, the grass in the meadow was pale yellow, and the fire marks on Half-Blood Hill stood out like ugly scars. Somebody had messed with my favourite place in the world, and I was not ... well, a happy camper.

As we made our way to the Big House, everybody from my years at camp. Nobody stopped to talk. Nobody said, "Welcome back."

Some did double takes when they saw Tyson, but most just walked grimly past and carried on with their duties – running messages, toting swords to sharpen on the grinding wheels. The camp felt like a military school. And believe me, I know. I've been kicked out of a couple.

None of that mattered to Tyson. He was absolutely fascinated by everything he saw. "Whasthat!" he gasped.

"The stables for pegasi," Percy said. "The winged horses."

"Whasthat!"

"Um ... those are the toilets."

"Whasthat!"

"The cabins for the campers. If they don't know who your Olympian parent is, they put you in the Hermes cabin – that brown one over there – until you're determined. Then, once they know, they put you in your dad or mom's group."

He looked at Percy in awe. "You ... have a cabin?"

"Number three." He pointed to a low grey building made of sea stone.

"You live with friends in the cabin?"

"No. No, just me." Percy didn't explain and neither did I. The embarrassing truth: he was the only one who stayed in that cabin because Percy wasn't supposed to be alive. The 'Big Three' gods – Zeus, Poseidon and Hades – had made a pact after World War II not to have any more children with mortals. They were more powerful than regular half-bloods. They were too unpredictable. When they got mad they tended to cause problems ... like World War II, for instance. The 'Big Three' pact had only been broken twice – once when Zeus sired Thalia, once when Poseidon sired Percy. Neither of them should've been born.

Thalia had got herself turned into a pine tree when she was twelve. Percy ... well, I was doing my best not to let him follow her example. I had dreams about what Poseidon might turn Percy into if he were ever on the verge of death – plankton, maybe. Or a floating patch of kelp. It gave me a good laugh when I was sad.

When we got to the Big House, we found Chiron in his apartment, listening to his favorite 1960s lounge music while he packed his saddlebags. I guess I should mention – Chiron is a centaur. From the waist up he looks like a regular middle-aged guy with curly brown hair and a scraggly beard. From the waist down, he's a white stallion. He can pass for human by compacting his lower half into a magic wheelchair. But most of the time, if the ceilings are high enough, he prefers hanging out in full centaur form.

Chiron couldn't be leaving. He's always trained demigods since literally forever. My stomach threatened to throw up everything I had eaten before, which wasn't much. Chiron was there for everything I ever did. Shooting my first bow, climbing the lava wall, everything. He was the only person I had left. Thalia, gone. Luke, betrayed. Grover, on a quest that could kill him. Percy, well, he won't make it very far. But Chiron, he was there and he will be there for me. He was like a father to me.

As soon as we saw him, Tyson froze. "Pony!" he cried in total rapture.

Chiron turned, looking offended. "I beg your pardon?"

I ran up and hugged him. "Chiron, what's happening? You're not ... leaving?" My voice was shaky. Chiron ruffled my hair and gave me a kindly smile.

"Hello, child. And Percy, my goodness. You've grown over the year!"

Percy swallowed. "Clarisse said you were ... you were..."

"Fired." Chiron's eyes glinted with dark humor.

"Ah, well, someone had to take the blame. Lord Zeus was most upset The tree he'd created from the spirit of his daughter, poisoned! Mr D had to punish someone."

"Besides himself, you mean," Percy growled. Just the thought of the camp director, Mr D, made me angry.

"But this is crazy!" I cried. "Chiron, you couldn't have had anything to do with poisoning Thalia's tree!"

"Nevertheless," Chiron sighed, "some in Olympus do not trust me now, under the circumstances."

"What circumstances?" Percy asked. Chiron's face darkened. He stuffed a Latin–English dictionary into his saddlebag while the Frank Sinatra music oozed from his boombox.

Tyson was still staring at Chiron in amazement. He whimpered like he wanted to pat Chiron's flank but was afraid to come closer. "Pony?" Chiron sniffed.

"My dear young Cyclops! I am a centaur."

"Chiron," Percy said. "What about the tree? What happened?"

He shook his head sadly. "The poison used on Thalia's pine is something from the Underworld, Percy. Some venom even I have never seen. It must have come from a monster quite deep in the pits of Tartarus."

"Then we know who's responsible. Kro–"

"Do not invoke the titan lord's name, Percy. Especially not here, not now."

"But last summer he tried to cause a civil war in Olympus! This has to be his idea. He'd get Luke to do it, that traitor."

"Perhaps," Chiron said. "But I fear I am being held responsible because I did not prevent it and I cannot cure it. The tree has only a few weeks of life left unless..."

"Unless what?" I asked eagerly. I'd do anything to cure Thalia's tree. To make Chiron stay.

"No," Chiron said. "A foolish thought. The whole valley is feeling the shock of the poison. The magical borders are deteriorating. The camp itself is dying. Only one source of magic would be strong enough to reverse the poison, and it was lost centuries ago."

"What is it?" Percy asked. "We'll go find it!"

Chiron closed his saddlebag. He pressed the STOP button on his boombox. Then he turned and rested his hand on Percy's shoulder, looking him straight in the eyes.

"Percy, you must promise me that you will not act rashly. I told your mother I did not want you to come here at all this summer. It's much too dangerous. But now that you are here, stay here. Train hard. Learn to fight. But do not leave."

"Why?" Percy asked. "I want to do something! I can't just let the borders fail. The whole camp will be –"

"Overrun by monsters," Chiron said. "Yes, I fear so. But you must not let yourself be baited into hasty action! This could be a trap of the titan lord. Remember last summer! He almost took your life."

It was true, but still, I wanted to help so badly. I also wanted to make Kronos pay. I mean, you'd think the titan lord would've learned his lesson aeons ago when he was overthrown by the gods. You'd think getting chopped into a million pieces and cast into the darkest part of the Underworld would give him a subtle clue that nobody wanted him around. But no. Because he was immortal, he was still alive down there in Tartarus – suffering in eternal pain, hungering to return and take revenge on Olympus. He couldn't act on his own, but he was great at twisting the minds of mortals and even gods to do his dirty work. The poisoning had to be his doing. Who else would be so low as to attack Thalia's tree, the only thing left of a hero who'd given her life to save her friends?

I was trying hard not to cry. Chiron couldn't see how upset I was over this. I needed to be strong for him. Also, Percy would probably make fun of me.

Chiron brushed a tear from my cheek. "Stay with Percy, child," he told me. "Keep him safe. The prophecy – remember it!"

"I-I will."

"Um..." Percy said. "Would this be the super-dangerous prophecy that has me in it, but the gods have forbidden you to tell me about?"

Nobody answered. "Right," Percy muttered. "Just checking."

"Chiron..." I said. "You told me the gods made you immortal only so long as you were needed to train heroes. If they dismiss you from camp –"

"Swear you will do your best to keep Percy from danger," he insisted. "Swear upon the River Styx."

"I-I swear it upon the River Styx," I said. Thunder rumbled outside.

"Very well," Chiron said. He seemed to relax just a little. "Perhaps my name will be cleared and I shall return. Until then, I go to visit my wild kinsmen in the Everglades. It's possible they know of some cure for the poisoned tree that I have forgotten. In any event, I will stay in exile until this matter is resolved ... one way or another."

I stifled a sob. Chiron patted my shoulder awkwardly. "There, now, child. I must entrust your safety to Mr D and the new activities director. We must hope ... well, perhaps they won't destroy the camp quite as quickly as I fear."

"Who is this Tantalus guy, anyway?" Percy demanded. "Where does he get off taking your job?"

A conch horn blew across the valley. I hadn't realized how late it was. It was time for the campers to assemble for dinner.

"Go," Chiron said. "You will meet him at the pavilion. I will contact your mother, Percy, and let her know you're safe. No doubt she'll be worried by now. Just remember my warning! You are in grave danger. Do not think for a moment that the titan lord has forgotten you!"

With that, he clopped out of the apartment and down the hall, Tyson calling after him, "Pony! Don't go!"

The best teacher I'd ever had was gone, maybe for good. Tyson started bawling almost as bad as I am. Percy tried to tell us that things would be okay, but I didn't believe it. The sun was setting behind the dining pavilion as the campers came up from their cabins. We stood in the shadow of a marble column and watched them file in.

I was still pretty shaken up, but I promised I'd talk to them later. Then I went off to join my siblings from the Athena cabin – a dozen boys and girls with blonde hair and grey eyes like mine.

I wasn't the oldest, but I'd been at camp more summers than just about anybody. You could tell that by looking at my camp necklace – one bead for every summer, and I had six. No one questioned my right to lead the line.

Next came Clarisse, leading the Ares cabin. She had one arm in a sling and a nasty-looking gash on her cheek, but otherwise her encounter with the bronze bulls didn't seem to have fazed her. Someone had taped a piece of paper to her back that said, YOU MOO, GIRL! But nobody in her cabin was bothering to tell her about it.

After the Ares kids came the Hephaestus cabin – six guys led by Charles Beckendorf, a big fifteen year-old African American kid. He had hands the size of catchers' mitts and a face that was hard and squinty from looking into a blacksmith's forge all day. He was nice enough once you got to know him, but no one ever called him Charlie or Chuck or Charles. Most just called him Beckendorf.

Rumor was he could make anything. Give him a chunk of metal and he could create a razor-sharp sword or a robotic warrior or a singing birdbath for your grandmother's garden. Whatever you wanted.

The other cabins filed in: Demeter, Apollo, Aphrodite, Dionysus. Naiads came up from the canoe lake. Dryads melted out of the trees.

From the meadow came a dozen satyrs, who reminded me painfully of Grover. I'd always had a soft spot for the satyrs. When they were at camp, they had to do all kinds of odd jobs for Mr D, the director, but their most important work was out in the real world.

They were the camp's seekers. They went undercover into schools all over the world, looking for potential half bloods and escorting them back to camp. That's how I'd met Grover. He had been the one to help me get to camp.

After the satyrs filed in to dinner, the Hermes cabin brought up the rear. They were always the biggest cabin.

Last summer, it had been led by Luke, the guy who'd fought with Thalia and me on top of Half-Blood Hill. Luke had befriended me... and then he'd tried to kill my friends. Now the Hermes cabin was led by Travis and Connor Stoll. They weren't twins, but they looked so much alike it didn't matter.

I could never remember which one was older. They were both tall and skinny, with mops of brown hair that hung in their eyes. They wore orange CAMP HALF-BLOOD t-shirts untucked over baggy shorts, and they had those elfish features all Hermes's kids had: upturned eyebrows, sarcastic smiles, a gleam in their eyes whenever they looked at you – like they were about to drop a firecracker down your shirt.

As soon as the last campers had filed in, Percy led Tyson into the middle of the pavilion. Conversations faltered. Heads turned.

"Who invited that?" Somebody at the Apollo table murmured. Percy glared in their direction, but he couldn't figure out who'd spoken.

From the head table a familiar voice drawled, "Well, well, if it isn't Peter Johnson. My millennium is complete."

I stifled a laugh.

"Percy Jackson ... sir."

Mr. D sipped his Diet Coke. "Yes. Well, as you young people say these days, whatever."

He was wearing his usual leopard-pattern Hawaiian shirt, walking shorts and tennis shoes with black socks. With his pudgy belly and his blotchy red face, he looked like a Las Vegas tourist who'd stayed up too late in the casinos. Behind him, a nervous-looking satyr was peeling the skins off grapes and handing them to Mr D one at a time. Mr D's real name is Dionysus. The god of wine. Zeus appointed him director of Camp Half-Blood to dry out for a hundred years – a punishment for chasing some off-limits wood nymph. Next to him, where Chiron usually sat (or stood, in centaur form), was someone I'd never seen before – a pale, horribly thin man in a threadbare orange prisoner's jumpsuit. The number over his pocket read 0001. He had blue shadows under his eyes, dirty fingernails and badly cut grey hair, like his last haircut had been done with a weed whacker.

He stared at Percy; he looked ... fractured. Angry and frustrated and hungry all at the same time.

"This boy," Dionysus told him, "you need to watch. Poseidon's child, you know."

"Ah!" the prisoner said. "That one."

His tone made it obvious that he and Dionysus had already discussed me at length.

"I am Tantalus," the prisoner said, smiling coldly. "On special assignment here until, well, until my Lord Dionysus decides otherwise. And you, Perseus Jackson, I do expect you to refrain from causing any more trouble."

"Trouble?" Percy demanded. Dionysus snapped his fingers. A newspaper appeared on the table – the front page of today's New York Post. There was his yearbook picture from Meriwether Prep. It was hard for me to make out the headline, but I had a pretty good guess what it said. Something like: Thirteen-Year-Old Lunatic Torches Gymnasium.

"Yes, trouble," Tantalus said with satisfaction. "You caused plenty of it last summer, I understand."

I snorted. Like it was his fault the gods had almost got into a civil war? A satyr inched forward nervously and set a plate of barbecued meat in front of Tantalus. The new activities director licked his lips. He looked at his empty goblet and said,

"Root beer. Barq's special stock. 1967."

The glass filled itself with foamy soda. Tantalus stretched out his hand hesitantly, as if he were afraid the goblet was hot.

"Go on, then, old fellow," Dionysus said, a strange sparkle in his eyes. "Perhaps now it will work."

Tantalus grabbed for the glass, but it scooted away before he could touch it. A few drops of root beer spilled, and Tantalus tried to dab them up with his fingers, but the drops rolled away like quicksilver before he could touch them. He growled and turned towards the plate of meat. He picked up a fork and tried to stab a piece of brisket, but the plate skittered down the table and flew off the end, straight into the coals of the brazier.

"Blast!" Tantalus muttered.

"Ah, well," Dionysus said, his voice dripping with false sympathy.

"Perhaps a few more days. Believe me, old chap, working at this camp will be torture enough. I'm sure your old curse will fade eventually."

"Eventually," muttered Tantalus, staring at Dionysus's Diet Coke. "Do you have any idea how dry one's throat gets after three thousand years?"

"You're that spirit from the Fields of Punishment," Percy said. "The one who stands in the lake with the fruit tree hanging over you, but you can't eat or drink."

Tantalus sneered at Percy. "A real scholar, aren't you, boy?"

"You must've done something really horrible when you were alive," Percy said, sounding mildly impressed.

"What was it?" Tantalus's eyes narrowed. Behind him, the satyrs were shaking their heads vigorously, trying to warn him.

"I'll be watching you, Percy Jackson," Tantalus said. "I don't want any problems at my camp."

"Your camp has problems already ... sir."

"Oh, go sit down, Johnson," Dionysus sighed. "I believe that table over there is yours – the one where no one else ever wants to sit."

Percy's face was burning, but I knew better than to talk back. Dionysus was an overgrown brat, but he was an immortal, superpowerful overgrown brat. Percy said, "Come on, Tyson."

"Oh, no," Tantalus said. "The monster stays here. We must decide what to do with it."

"Him," Percy snapped. "His name is Tyson."

The new activities director raised an eyebrow.

"Tyson saved the camp," Percy insisted. "He pounded those bronze bulls. Otherwise they would've burned down this whole place."

"Yes," Tantalus sighed, "and what a pity that would've been."

Dionysus snickered.

"Leave us," Tantalus ordered, "while we decide this creature's fate." Tyson looked at Percy with fear in his one big eye.

"I'll be right over here, big guy," Percy promised. "Don't worry. We'll find you a good place to sleep tonight."

Tyson nodded. "I believe you. You are my friend."

I turned back to my siblings as Percy trudged over to the Poseidon table and slumped onto the bench. A wood nymph brought me a plate of Olympian olive-and-pepperoni pizza, but I wasn't hungry. I'd been almost today. Camp Half-Blood was in serious trouble and Chiron had told me not to do anything about it. I didn't think things could get much worse. But then Tantalus had one of the satyrs blow the conch horn to get our attention for announcements.

"Yes, well," Tantalus said, once the talking had died down. "Another fine meal! Or so I am told."

As he spoke, he inched his hand towards his refilled dinner plate, as if maybe the food wouldn't notice what he was doing, but it did. It shot away down the table as soon as he got within twenty centimeters.

"And here on my first day of authority," he continued as if nothing had happened, "I'd like to say what a pleasant form of punishment it is to be here. Over the course of the summer, I hope to torture, er, interact with each and every one of you children. You all look good enough to eat."

Dionysus clapped politely, leading to some half-hearted applause from the satyrs. Tyson was still standing at the head table, looking uncomfortable, but every time he tried to scoot out of the limelight, Tantalus pulled him back. "And now some changes!"

Tantalus gave the campers a crooked smile. "We are reinstituting the chariot races!" Murmuring broke out at all the tables – excitement, fear, disbelief.

"Now I know," Tantalus continued, raising his voice, "that these races were discontinued some years ago due to, ah, technical problems."

"Three deaths and twenty-six mutilations," someone at the Apollo table called.

"Yes, yes!" Tantalus said. "But I know that you will all join me in welcoming the return of this camp tradition. Golden laurels will go to the winning charioteers each month. Teams may register in the morning! The first race will be held in three days' time. We will release you from most of your regular activities to prepare your chariots and choose your horses. Oh, and did I mention, the victorious team's cabin will have no chores for the month in which they win?"

An explosion of excited conversation – no KP for a whole month? No stable cleaning? Was he serious? Then the last person I expected to object did so.

"But, sir!" Clarisse said. She looked nervous, but she stood up to speak from the Ares table. Some of the campers snickered when they saw the YOU MOO, GIRL! sign on her back. "What about patrol duty? I mean, if we drop everything to ready our chariots –"

"Ah, the hero of the day," Tantalus exclaimed. "Brave Clarisse, who single-handedly bested the bronze bulls!"

Clarisse blinked, then blushed. "Um, I didn't –"

"And modest, too." Tantalus grinned. "Not to worry, my dear! This is a summer camp. We are here to enjoy ourselves, yes?"

"But the tree –"

"And now," Tantalus said, as several of Clarisse's cabin mates pulled her back into her seat, "before we proceed to the campfire and sing-along, one slight housekeeping issue. Percy Jackson and Annabeth Chase have seen fit, for some reason, to bring this here."

Tantalus waved a hand towards Tyson. Uneasy murmuring spread among the campers. A lot of sideways looks at me. I wanted to kill Tantalus. "Now, of course," he said, "Cyclopes have a reputation for being bloodthirsty monsters with a very small brain capacity. Under normal circumstances, I would release this beast into the woods and have you hunt it down with torches and pointed sticks. But who knows? Perhaps this Cyclops is not as horrible as most of its brethren. Until it proves worthy of destruction, we need a place to keep it! I've thought about the stables, but that will make the horses nervous. Hermes's cabin, possibly?"

Silence at the Hermes table. Travis and Connor Stoll developed a sudden interest in the tablecloth. I couldn't blame them. The Hermes cabin was always full to bursting. There was no way they could take in a two-meter Cyclops.

"Come now," Tantalus chided. "The monster may be able to do some menial chores. Any suggestions as to where such a beast should be kennelled?"

Suddenly everybody gasped. Tantalus scooted away from Tyson in surprise. All I could do was stare in disbelief at the brilliant green light – a dazzling holographic image that had appeared above Tyson's head. With a sickening twist in my stomach, I remembered what I had said to Percy about Cyclopes, They're the children of nature spirits and gods ... Well, one god in particular, usually ... Swirling over Tyson was a glowing green trident – the same symbol that had appeared above Percy the day Poseidon had claimed him as his son.

There was a moment of awed silence. Being claimed was a rare event. Some campers waited in vain for it their whole lives. When Percy had been claimed by Poseidon last summer, everyone had reverently knelt. But now, they followed Tantalus's lead, and Tantalus roared with laughter.

"Well! I think we know where to put the beast now. By the gods, I can see the family resemblance!"

Everybody laughed except me and a few of my other friends. Tyson didn't seem to notice. He was too mystified, trying to swat the glowing trident that was now fading over his head. He was too innocent to understand how much they were making fun of him, how cruel people were. But I got it. Percy had a new cabin mate. He had a monster for a half-brother.

A/N: school's been hard lately so posting chapters is going to have weird schedules and im really sorry about that!