They belted it out like a quarterback calling a play.

"What do you mean?" I said. "That makes no sense!"

"30, 31, 75, 12!" Anger wailed. "That's all we can tell you. Now give us the eye! Almost to camp!"

We were off the highway now, zipping through the countryside of northern Long Island. I could see Half-Blood Hill ahead of us, with its giant pine tree at the crest—Thalia's tree, which contained the life force or a fallen hero.

"Percy!" Annabeth said more urgently. "Give them the eye now!"

I decided not to argue. I threw the eye into Wasp's lap.

The old lady snatched it up, pushed it into her eye socket like somebody putting in a contact lens, and blinked. "Whoa!"

She slammed on the brakes. The taxi spun four or five times in a cloud of smoke and squealed to a halt in the middle of the farm road at the base of Half-Blood Hill.

Tyson let loose a huge belch. "Better now."

"All right," I told the Gray Sisters. "Now tell me what those numbers mean."

"No time!" Annabeth opened her door. "We have to get out now."

I was about to ask why, when I looked up at Half-Blood Hill and understood.

At the crest of the hill was a group of campers. And they were under attack.

Mythologically speaking, if there's anything I hate worse than trios of old ladies, it's bulls. Last summer, I fought the Minotaur on top of Half-Blood Hill. This time what I saw up there was even worse: two bulls. And not just regular bulls—bronze ones the size of elephants. And even that wasn't bad enough. Naturally they had to breathe fire, too.

As soon as we exited the taxi, the Gray Sisters peeled out, heading back to New York, where life was safer. They didn't even wait for their extra three-drachma payment. They just left us on the side of the road, Annabeth with nothing but her backpack and knife, Tyson and me still in our burned-up tie-dyed gym clothes.

"Oh, man," said Annabeth, looking at the battle raging on the hill.

What worried me most weren't the bulls themselves. Or the ten heroes in full battle armor who were getting their bronze-plated booties whooped. What worried me was that the bulls were ranging all over the hill, even around the back side of the pine tree. That shouldn't have been possible. The camp's magic boundaries didn't allow monsters to cross past Thalia's tree. But the metal bulls were doing it anyway.

One of the heroes shouted, "Border patrol, to me!" A girl's voice—gruff and familiar.

Border patrol? I thought. The camp didn't have a border patrol.

"It's Clarisse," Annabeth said. "Come on, we have to help her."

Normally, rushing to Clarisse's aid would not have been high on my "to do" list. She was one of the biggest bullies at camp. The first time we'd met she tried to introduce my head to a toilet. She was also a daughter of Ares, and I'd had a very serious disagreement with her father last summer, so now the god of war and all his children basically hated my guts.

Still, she was in trouble. Her fellow warriors were scattering, running in panic as the bulls charged. The grass was burning in huge swathes around the pine tree. One hero screamed and waved his arms as he ran in circles, the horsehair plume on his helmet blazing like a fiery Mohawk. Clarisse's own armor was charred. She was fighting with a broken spear shaft, the other end embedded uselessly in the metal joint of one bull's shoulder.

I uncapped my ballpoint pen. It shimmered, growing longer and heavier until I held the bronze sword Anaklusmos in my hands. "Tyson, stay here. I don't want you taking any more chances."

"No!" Annabeth said. "We need him."

I stared at her. "He's mortal. He got lucky with the dodge balls but he can't—"

"Percy, do you know what those are up there? The Colchis bulls, made by Hephaestus himself. We can't fight them without Medea's Sunscreen SPF 50,000. We'll get burned to a crisp."

"Medea's what?"

Annabeth rummaged through her backpack and cursed. "I had a jar of tropical coconut scent sitting on my night-stand at home. Why didn't I bring it?"

I'd learned a long time ago not to question Annabeth too much. It just made me more confused. "Look, I don't know what you're talking about, but I'm not going to let Tyson get fried."

"Percy—"

"Tyson, stay back." I raised my sword. "I'm going in."

Tyson tried to protest, but I was already running up the hill toward Clarisse, who was yelling at her patrol, trying to get them into phalanx formation. It was a good idea. The few who were listening lined up shoulder-to-shoulder, locking their shields to form an ox-hide—and-bronze wall, their spears bristling over the top like porcupine quills.

Unfortunately, Clarisse could only muster six campers. The other four were still running around with their helmets on fire. Annabeth ran toward them, trying to help. She taunted one of the bulls into chasing her, then turned invisible, completely confusing the monster. The other bull charged Clarisse's line.

I was halfway up the hill—not close enough to help. Clarisse hadn't even seen me yet.

The bull moved deadly fast for something so big. Its metal hide gleamed in the sun. It had fist-sized rubies for eyes, and horns of polished silver. When it opened its hinged mouth, a column of white-hot flame blasted out.

"Hold the line!" Clarisse ordered her warriors.

Whatever else you could say about Clarisse, she was brave. She was a big girl with cruel eyes like her father's. She looked like she was born to wear Greek battle armor, but I didn't see how even she could stand against that bull's charge.

Unfortunately, at that moment, the other bull lost interest in finding Annabeth. It turned, wheeling around behind Clarisse on her unprotected side.

"Behind you!" I yelled. "Look out!"

I shouldn't have said anything, because all I did was startle her. Bull Number One crashed into her shield, and the phalanx broke. Clarisse went flying backward and landed in a smoldering patch of grass. The bull charged past her, but not before blasting the other heroes with its fiery breath. Their shields melted right off their arms. They dropped their weapons and ran as Bull Number Two closed in on Clarisse for the kill.

I lunged forward and grabbed Clarisse by the straps of her armor. I dragged her out of the way just as Bull Number Two freight-trained past. I gave it a good swipe with Riptide and cut a huge gash in its flank, but the monster just creaked and groaned and kept on going.

It hadn't touched me, but I could feel the heat of its metal skin. Its body temperature could've microwaved a frozen burrito.

"Let me go!" Clarisse pummeled my hand. "Percy, curse you!"

I dropped her in a heap next to the pine tree and turned to face the bulls. We were on the inside slope of the hill now, the valley of Camp Half-Blood directly below us—the cabins, the training facilities, the Big House—all of it at risk if these bulls got past us.

Annabeth shouted orders to the other heroes, telling them to spread out and keep the bulls distracted.

Bull Number One ran a wide arc, making its way back toward me. As it passed the middle of the hill, where the invisible boundary line should've kept it out, it slowed down a little, as if it were struggling against a strong wind; but then it broke through and kept coming. Bull Number Two turned to face me, fire sputtering from the gash I'd cut in its side. I couldn't tell if it felt any pain, but its ruby eyes seemed to glare at me like I'd just made things personal.

I couldn't fight both bulls at the same time. I'd have to take down Bull Number Two first, cut its head off before Bull Number One charged back into range. My arms already felt tired. I realized how long it had been since I'd worked out with Riptide, how out of practice I was.