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.”

I looked nervously at Annabeth, then at the groups of girls who were roaming the gym.

“Well?” Annabeth said.

“Um, who should I ask?”

She punched me in the gut. “Me, Seaweed Brain.”

“Oh. Oh, right.”

So we went onto the dance floor, and I looked over to see how Thalia and Grover were doing things. I put one hand on Annabeth’s hip, and she clasped my other hand like she was about to judo throw me.

“I’m not going to bite,” she told me. “Honestly, Percy. Don’t you guys have dances at your school?”

I didn’t answer. The truth was we did. But I’d never, like, actually danced at one. I was usually one of the guys playing basketball in the corner.

We shuffled around for a few minutes. I tried to concentrate on little things, like the crepe-paper streamers and the punch bowl—anything but the fact that Annabeth was taller than me, and my hands were sweaty and probably gross, and I kept stepping on her toes.

“What were you saying earlier?” I asked. “Are you having trouble at school or something?”

She pursed her lips. “It’s not that. It’s my dad.”

“Uh-oh.” I knew Annabeth had a rocky relationship with her father. “I thought it was getting better with you two. Is it your stepmom again?”

Annabeth sighed. “He decided to move. Just when I was getting settled in New York, he took this stupid new job researching for a World War I book. In San Francisco.”

She said this the same way she might say Fields of Punishment or Hades’s gym shorts.

“So he wants you to move out there with him?” I asked.

“To the other side of the country,” she said miserably. “And half-bloods can’t live in San Francisco. He should know that.”

“What? Why not?”

Annabeth rolled her eyes. Maybe she thought I was kidding. “You know. It’s right there.”

“Oh,” I said. I had no idea what she was talking about, but I didn’t want to sound stupid. “So . . . you’ll go back to living at camp or what?”

“It’s more serious than that, Percy. I . . . I probably should tell you something.”

Suddenly she froze. “They’re gone.”

“What?”

I followed her gaze. The bleachers. The two half-blood kids, Bianca and Nico, were no longer there. The door next to the bleachers was wide open. Dr. Thorn was nowhere in sight.

“We have to get Thalia and Grover!” Annabeth looked around frantically. “Oh, where’d they dance off to? Come on!”

She ran through the crowd. I was about to follow when a mob of girls got in my way. I maneuvered around them to avoid getting the ribbon-and-lipstick treatment, and by the time I was free, Annabeth had disappeared. I turned a full circle, looking for her or Thalia and Grover. Instead, I saw something that chilled my blood.

About fifty feet away, lying on the gym floor, was a floppy green cap just like the one Bianca di Angelo had been wearing. Near it were a few scattered trading cards. Then I caught a glimpse of Dr. Thorn. He was hurrying out a door at the opposite end of the gym, steering the di Angelo kids by the scruffs of their necks, like kittens.

I still couldn’t see Annabeth, but I knew she’d be heading the other way, looking for Thalia and Grover.

I almost ran after her, and then I thought, Wait.

I remembered what Thalia had said to me in the entry hall, looking at me all puzzled when I asked about the finger-snap trick: Hasn’t Chiron shown you how to do that yet? I thought about the way Grover had turned to her, expecting her to save the day.

Not that I resented Thalia. She was cool. It wasn’t her fault her dad was Zeus and she got all the attention. . . . Still, I didn’t need to run after her to solve every problem. Besides, there wasn’t time. The di Angelos were in danger. They might be long gone by the time I found my friends. I knew monsters. I could handle this myself.

I took Riptide out of my pocket and ran after Dr. Thorn.

* * *

The door led into a dark hallway. I heard sounds of scuffling up ahead, then a painful grunt. I uncapped Riptide.

The pen grew in my hands until I held a bronze Greek sword about three-feet long with a leather-bound grip. The blade glowed faintly, casting a golden light on the rows of lockers.

I jogged down the corridor, but when I got to the other end, no one was there. I opened a door and found myself back in the main entry hall. I was completely turned around. I didn’t see Dr. Thorn anywhere, but there on the opposite side of the room were the di Angelo kids. They stood frozen in horror, staring right at me.

I advanced slowly, lowering the tip of my sword. “It’s okay. I’m not going to hurt you.”

They didn’t answer. Their eyes were full of fear. What was wrong with them? Where was Dr. Thorn? Maybe he’d sensed the presence of Riptide and retreated. Monsters hated celestial bronze weapons.

“My name’s Percy,” I said, trying to keep my voice level. “I’m going to take you out of here, get you somewhere safe.”

Bianca’s eyes widened. Her fists clenched. Only too late did I realize what her look meant. She wasn’t afraid of me. She was trying to warn me.

I whirled around and something went WHIIISH! Pain exploded in my shoulder. A force like a huge hand yanked me backward and slammed me to the wall.

I slashed with my sword but there was nothing to hit.

A cold laugh echoed through the hall.

“Yes, Perseus Jackson,” Dr. Thorn said. His accent mangled the J in my last name. “I know who you are.”

I tried to free my shoulder. My coat and shirt were pinned to the wall by some kind of spike—a black dagger-like projectile about a foot long. It had grazed the skin of my shoulder as it passed through my clothes, and the cut burned. I’d felt something like this before. Poison.