The end of the world started when a pegasus landed on the hood of my car.

Up until then, I was having a great afternoon. Technically I wasn't supposed to be driving because I wouldn't turn sixteen for another week, but my mom and my stepdad, Paul, took my friend Rachel and me to this private stretch of beach on the South Shore, and Paul let us borrow his Prius for a short spin.

Now, I know you're thinking, Wow, that was really irresponsible of him, blah, blah, blah, but Paul knows me pretty well. He's seen me slice up demons and leap out of exploding school buildings, so he probably figured taking a car a few hundred yards wasn't exactly the most dangerous thing I'd ever done.

Anyway, Rachel and I were driving along. It was a hot August day. Rachel's red hair was pulled back in a ponytail and she wore a white blouse over her swimsuit. I'd never seen her in anything but ratty T-shirts and paint-splattered jeans before, and she looked like a million golden drachmas.

"Oh, pull up right there!" she told me.

We parked on a ridge overlooking the Atlantic. The sea is always one of my favorite places, but today it was especially nice—glittery green and smooth as glass, as though my dad was keeping it calm just for us.

My dad, by the way, is Poseidon. He can do stuff like that.

"So." Rachel smiled at me. "About that invitation."

"Oh . . . right." I tried to sound excited. I mean, she'd asked me to her family's vacation house on St. Thomas for three days. I didn't get a lot of offers like that. My family's idea of a fancy vacation was a weekend in a rundown cabin on Long Island with some movie rentals and a couple of frozen pizzas, and here Rachel's folks were willing to let me tag along to the Caribbean.

Besides, I seriously needed a vacation. This summer had been the hardest of my life. The idea of taking a break even for a few days was really tempting.

Still, something big was supposed to go down any day now. I was "on call" for a mission. Even worse, next week was my birthday. There was this prophecy that said when I turned sixteen, bad things would happen.

"Percy," she said, "I know the timing is bad. But it's always bad for you, right?"

She had a point.

"I really want to go," I promised. "It's just—"

"The war.”

I nodded. I didn't like talking about it, but Rachel knew. Unlike most mortals, she could see through the Mist—the magic veil that distorts human vision. She'd seen monsters. She'd met some of the other demigods who were fighting the Titans and their allies. She'd even been there last summer when the chopped-up Lord Kronos rose out of his coffin in a terrible new form, and she'd earned my permanent respect by nailing him in the eye with a blue plastic hairbrush.

She put her hand on my arm. "Just think about it, okay? We don't leave for a couple of days. My dad . . ." Her voice faltered.

"Is he giving you a hard time?" I asked.

Rachel shook her head in disgust. "He's trying to be nice to me, which is almost worse. He wants me to go to Clarion Ladies Academy m the fall."

"The school where your mom went?"

"It's a stupid finishing school for society girls, all the way in New Hampshire. Can you see me in finishing school?"

I admitted the idea sounded pretty dumb. Rachel was into urban art projects and feeding the homeless and going to protest rallies to "Save the Endangered Yellow-bellied Sapsucker" and stuff like that. I'd never even seen her wear a dress. It was hard to imagine her learning to be a socialite.

She sighed. "He thinks if he does a bunch of nice stuff for me, I'll feel guilty and give in."

"Which is why he agreed to let me come with you guys on vacation?"

"Yes . . . but Percy, you'd be doing me a huge favor. It would be so much better if you were with us. Besides, there's something I want to talk—" She stopped abruptly.

"Something you want to talk about?" I asked. "You mean . . . so serious we'd have to go to St. Thomas to talk about it?"

She pursed her lips. "Look, just forget it for now. Let's pretend we're a couple of normal people. We're out for a drive, and we're watching the ocean, and it's nice to be together."

I could tell something was bothering her, but she put on a brave smile. The sunlight made her hair look like fire.

We'd spent a lot of time together this summer. I hadn't exactly planned it that way, but the more serious things got at camp, the more I found myself needing to call up Rachel and get away, just for some breathing room. I needed to remind myself that the mortal world was still out there, away from all the monsters using me as their personal punching bag.

"Okay," I said. "Just a normal afternoon and two normal people."

She nodded. "And so . . . hypothetically, if these two people liked each other, what would it take to get the stupid guy to kiss the girl, huh?"

"Oh . . ." I felt like one of Apollo's sacred cows—slow, dumb, and bright red. "Um . . ."

I can't pretend I hadn't thought about Rachel. She was so much easier to be around than . . . well, than some other girls I knew. I didn't have to work hard, or watch what I said, or rack my brain trying to figure out what she was thinking. Rachel didn't hide much. She let you know how she felt.

I'm not sure what I would have done next—but I was so distracted, I didn't notice the huge black form swooping down from the sky until four hooves landed on the hood of the Prius with a WUMP-WUMP-CRUNCH!

Hey, boss, a voice said in my head. Nice car!

Blackjack the pegasus was an old friend of mine, so I tried not to get too annoyed by the craters he'd just put in the hood; but I didn't think my stepdad would be real stoked.

"Blackjack," I sighed. "What are you—"

Then I saw who was riding on his back, and I knew my day was about to get a lot more complicated.

" 'Sup, Percy."

Charles Beckendorf, senior counselor for the Hephaestus cabin, would make most monsters cry for their mommies. He was huge, with ripped muscles from working on the forges every summer, two years older than me, and one of the camp's best armorsmiths. He made some seriously ingenious mechanical stuff. A month before, he'd rigged a Greek firebomb in the bathroom of a tour bus that was carrying a bunch of monsters across country. The explosion took out a whole legion of Kronos's evil meanies as soon as the first harpy went flush.

Beckendorf was dressed for combat. He wore a bronze breastplate and war helm with black camo pants and a sword strapped to his side. His explosives bag was slung over his shoulder.

"Time?" I asked.

He nodded grimly.

A clump formed in my throat. I'd known this was coming. We'd been planning for it for weeks, but I'd half hoped it would never happen.

Rachel looked up at Beckendorf. "Hi."

"Oh, hey. I'm Beckendorf. You must be Rachel. Percy's told me . . . uh, I mean he mentioned you."

Rachel raised an eyebrow. "Really? Good." She glanced at Blackjack, who was clopping his hooves against the hood of the Prius. "So I guess you guys have to go save the world now."

"Pretty much," Beckendorf agreed.

I looked at Rachel helplessly. "Would you tell my mom—"

"I'll tell her. I'm sure she's used to it. And I'll explain to Paul about the hood."

I nodded my thanks. I figured this might be the last time Paul loaned me his car.

"Good luck." Rachel kissed me before I could even react. "Now, get going, half-blood. Go kill some monsters for me."