"You mean the Mist? Hasn't Chiron shown you how to do that yet?"

An uncomfortable lump formed in my throat. Chiron was our head trainer at camp, but he'd never shown me anything like that. Why had he shown Thalia and not me?

Grover hurried us to a door that had GYM written on the glass. Even with my dyslexia, I could read that much.

"That was close!" Grover said. "Thank the gods you got here!"

Annabeth and Thalia both hugged Grover. I gave him a big high five.

It was good to see him after so many months. He'd gotten a little taller and had sprouted a few more whiskers, but otherwise he looked like he always did when he passed for human—a red cap on his curly brown hair to hide his goat horns, baggy jeans and sneakers with fake feet to hide his furry legs and hooves. He was wearing a black T-shirt that took me a few seconds to read. It said WESTOVER HALL: GRUNT. I wasn't sure whether that was, like, Grover's rank or maybe just the school motto.

"So what's the emergency?" I asked.

Grover took a deep breath. "I found two."

"Two half-bloods?" Thalia asked, amazed. "Here?"

Grover nodded.

Finding one half-blood was rare enough. This year, Chiron had put the satyrs on emergency overtime and sent them all over the country, scouring schools from fourth grade through high school for possible recruits. These were desperate times. We were losing campers. We needed all the new fighters we could find. The problem was, there just weren't that many demigods out there.

"A brother and a sister," he said. "They're ten and twelve. I don't know their parentage, but they're strong. We're running out of time, though. I need help."

"Monsters?"

One." Grover looked nervous. "He suspects. I don't think he's positive yet, but this is the last day of term. I'm sure he won't let them leave campus without finding out. It may be our last chance! Every time I try to get close to them, he's always there, blocking me. I don't know what to do!"

Grover looked at Thalia desperately. I tried not to feel upset by that. Used to be, Grover looked to me for answers, but Thalia had seniority. Not just because her dad was Zeus. Thalia had more experience than any of us with fending off monsters in the real world.

"Right," she said. "These half-bloods are at the dance?"

Grover nodded.

"Then let's dance," Thalia said. "Who's the monster?"

"Oh," Grover said, and looked around nervously. "You just met him. The vice principal, Dr. Thorn."

Weird thing about military schools: the kids go absolutely nuts when there's a special event and they get to be out of uniform. I guess it's because everything's so strict the rest of the time, they feel like they've got to overcompensate or something.

There were black and red balloons all over the gym floor, and guys were kicking them in each others faces, or trying to strangle each other with the crepe-paper streamers taped to the walls. Girls moved around in football huddles, the way they always do, wearing lots of makeup and spaghetti-strap tops and brightly colored pants and shoes that looked like torture devices. Every once in a while they'd surround some poor guy like a pack of piranhas, shrieking and giggling, and when they finally moved on, the guy would have ribbons in his hair and a bunch of lipstick graffiti all over his face. Some of the older guys looked more like me—uncomfortable, hanging out at the edges of the gym and trying to hide, like any minute they might have to fight for their lives. Of course, in my case, it was true…

"There they are." Grover nodded toward a couple of younger kids arguing in the bleachers. "Bianca and Nico di Angela"

The girl wore a floppy green cap, like she was trying to hide her face. The boy was obviously her little brother. They both had dark silky hair and olive skin, and they used their hands a lot as they talked. The boy was shuffling some kind of trading cards. His sister seemed to be scolding him about something. She kept looking around like she sensed something was wrong.

Annabeth said, "Do they… I mean, have you told them?"

Grover shook his head. "You know how it is. That could put them in more danger. Once they realize who they are, their scent becomes stronger."

He looked at me, and I nodded. I'd never really understood what half-bloods «smell» like to monsters and satyrs, but I knew that your scent could get you killed. And the more powerful a demigod you became, the more you smelled like a monster's lunch.

"So let's grab them and get out of here," I said.

I started forward, but Thalia put her hand on my shoulder. The vice principal, Dr. Thorn, had slipped out of a doorway near the bleachers and was standing near the di Angelo siblings. He nodded coldly in our direction. His blue eye seemed to glow.

Judging from his expression, I guessed Thorn hadn't been fooled by Thalia's trick with the Mist after all. He suspected who we were. He was just waiting to see why we were here.

"Don't look at the kids," Thalia ordered. "We have to wait for a chance to get them. We need to pretend we're not interested in them. Throw him off the scent."

"How?"

"We're three powerful half-bloods. Our presence should confuse him. Mingle. Act natural. Do some dancing. But keep an eye on those kids."

"Dancing?" Annabeth asked.

Thalia nodded. She cocked her ear to the music and made a face. "Ugh. Who chose the Jesse McCartney?"

Grover looked hurt. "I did."

"Oh my gods, Grover. That is so lame. Can't you play, like, Green Day or something?"

"Green who?"

"Never mind. Let's dance."

"But I can't dance!"

"You can if I'm leading," Thalia said. "Come on, goat boy."

Grover yelped as Thalia grabbed his hand and led him onto the dance floor.

Annabeth smiled.

"What?" I asked.

"Nothing. It's just cool to have Thalia back."

Annabeth had grown taller than me since last summer, which I found kind of disturbing. She used to wear no jewelry except for her Camp Half-Blood bead necklace, but now she wore little silver earrings shaped like owls—the symbol of her mother, Athena. She pulled off her ski cap, and her long blond hair tumbled down her shoulders. It made her look older, for some reason.

"So…" I tried to think of something to say. Act natural, Thalia had told us. When you're a half-blood on a dangerous mission, what the heck is natural? "Um, design any good buildings lately?"

Annabeth's eyes lit up, the way they always did when she talked about architecture. "Oh my gods, Percy. At my new school, I get to take 3-D design as an elective, and there's this cool computer program…"

She went on to explain how she'd designed this huge monument that she wanted to build at Ground Zero in Manhattan. She talked about structural supports and facades and stuff, and I tried to listen. I knew she wanted to be a super architect when she grew up—she loves math and historical buildings and all that—but I hardly understood a word she was saying.

The truth was I was kind of disappointed to hear that she liked her new school so much. It was the first time she'd gone to school in New York. I'd been hoping to see her more often. It was a boarding school in Brooklyn, and she and Thalia were both attending, close enough to Camp Half-Blood that Chiron could help if they got in any trouble. Because it was an all-girls school, and I was going to MS-54 in Manhattan, I hardly ever saw them.

Yeah, uh, cool," I said. "So you're staying there the rest of the year, huh?"

Her face got dark. "Well, maybe, if I don't—"

"Hey!" Thalia called to us. She was slow dancing with Grover, who was tripping all over himself, kicking Thalia in the shins, and looking like he wanted to die. At least his feet were fake. Unlike me, he had an excuse for being clumsy.

"Dance, you guys!" Thalia ordered. "You look stupid just standing there."