"Wait," Thalia said. She started rifling through her backpack. "There is somebody in San Francisco who can help us. I've got the address here somewhere."

"Who?" I asked.

Thalia pulled out a crumpled piece of notebook paper and held it up. "Professor Chase. Annabeth's dad."

After hearing Annabeth gripe about her dad for two years, I was expecting him to have devil horns and fangs. I was not expecting him to be wearing an old-fashioned aviator's cap and goggles. He looked so weird, with his eyes bugging out through the glasses, that we all took a step back on the front porch.

"Hello," he said in a friendly voice, "Are you delivering my airplanes?"

Thalia, Zoe, and I looked at each other warily.

"Um, no, sir," I said.

"Drat," he said. "I need three more Sopwith Camels."

"Right," I said, though I had no clue what he was talking about. "We're friends of Annabeth."

"Annabeth?" He straightened as if I'd just given him an electric shock. "Is she all right? Has something happened?"

None of us answered, but our faces must've told him that something was very wrong. He took off his cap and goggles. He had sandy-colored hair like Annabeth and intense brown eyes. He was handsome, I guess, for an older guy, but it looked like he hadn't shaved in a couple of days, and his shirt was buttoned wrong, so one side of his collar stuck up higher than the other side.

"You'd better come in," he said.

It didn't look like a house they'd just moved into. There were LEGO robots on the stairs and two cats sleeping on the sofa in the living room. The coffee table was stacked with magazines, and a little kid's winter coat was spread on the floor. The whole house smelled like fresh-baked chocolate-chip cookies. There was jazz music coming from the kitchen. It seemed like a messy, happy kind of home—the kind of place that had been lived in forever.

"Dad!" a little boy screamed. "He's taking apart my robots!"

"Bobby," Dr. Chase called absently, "don't take apart your brother's robots."

"I'm Bobby," the little boy protested. "He's Matthew!"

"Matthew," Dr. Chase called, "don't take apart your brother's robots!"

"Okay, Dad!"

Dr. Chase turned to us. "We'll go upstairs to my study. This way."

"Honey?" a woman called. Annabeth's stepmom appeared in the living room, wiping her hands on a dish towel. She was a pretty Asian woman with red highlighted hair tied in a bun.

"Who are our guests?" she asked.

"Oh," Dr. Chase said. "This is…"

He stared at us blankly.

"Frederick," she chided. "You forgot to ask them their names?"

We introduced ourselves a little uneasily, but Mrs. Chase seemed really nice. She asked if we were hungry. We admitted we were, and she told us she'd bring us some cookies and sandwiches and sodas.

"Dear," Dr. Chase said. "They came about Annabeth."

I half expected Mrs. Chase to turn into a raving lunatic at the mention of her stepdaughter, but she just pursed her lips and looked concerned. "All right. Go on up to the study and I'll bring you some food." She smiled at me. "Nice meeting you, Percy. I've heard a lot about you."

Upstairs, we walked into Dr. Chase's study and I said, "Whoa!"

The room was wall-to-wall books, but what really caught my attention were the war toys. There was a huge table with miniature tanks and soldiers fighting along a blue painted river, with hills and fake trees and stuff. Old-fashioned biplanes hung on strings from the ceiling, tilted at crazy angles like they were in the middle of a dogfight.

Dr. Chase smiled. "Yes. The Third Battle of Ypres. I'm writing a paper, you see, on the use of Sopwith Camels to strafe enemy lines. I believe they played a much greater role than they've been given credit for."

He plucked a biplane from its string and swept it across the battlefield, making airplane engine noises as he knocked down little German soldiers.

"Oh, right," I said. I knew Annabeth's dad was a professor of military history. She'd never mentioned he played with toy soldiers.

Zoe came over and studied the battlefield. "The German lines were farther from the river."

Dr. Chase stared at her. "How do you know that?"

"I was there," she said matter-of-factly. "Artemis wanted to show us how horrible war was, the way mortal men fight each other. And how foolish, too. The battle was a complete waste."

Dr. Chase opened his mouth in shock. "You—"

"She's a Hunter, sir," Thalia said. "But that's not why we're here. We need—"

"You saw the Sopwith Camels?" Dr. Chase said. "How many were there? What formations did they fly?"

"Sir," Thalia broke in again. "Annabeth is in danger."

That got his attention. He set the biplane down.

"Of course," he said. "Tell me everything."

It wasn't easy, but we tried. Meanwhile, the afternoon light was fading outside. We were running out of time.

When we'd finished, Dr. Chase collapsed in his leather recliner. He laced his hands. "My poor brave Annabeth. We must hurry."

"Sir, we need transportation to Mount Tamalpais," Zoe said. "And we need it immediately."

"I'll drive you. Hmm. it would be faster to fly in my Camel, but it only seats two."

"Whoa, you have an actual biplane?" I said.

"Down at Crissy Field," Dr. Chase said proudly. "That's the reason I had to move here. My sponsor is a private collector with some of the finest World War I relics in the world. He let me restore the Sopwith Camel—"

"Sir," Thalia said. "Just a car would be great. And it might be better if we went without you. It's too dangerous." .

Dr. Chase frowned uncomfortably. "Now wait a minute, young lady. Annabeth is my daughter. Dangerous or not, I… I can't just—"

"Snacks," Mrs. Chase announced. She pushed through the door with a tray full of peanut-butter-and-jelly sandwiches and Cokes and cookies fresh out of the oven, the chocolate chips still gooey. Thalia and I inhaled a few cookies while Zoe said, "I can drive, sir. I'm not as young as I look. I promise not to destroy your car."

Mrs. Chase knit her eyebrows. "What's this about?"

"Annabeth is in danger," Dr. Chase said. "On Mount Tam. I would drive them, but… apparently it's no place for mortals."

It sounded like it was really hard for him to get that last part out.

I waited for Mrs. Chase to say no. I mean, what mortal parent would allow three underage teenagers to borrow their car? To my surprise, Mrs. Chase nodded. "Then they'd better get going."

"Right!" Dr. Chase jumped up and started patting his pockets. "My keys…"

His wife sighed. "Frederick, honestly. You'd lose your head if it weren't wrapped inside your aviator hat. The keys are hanging on the peg by the front door."

"Right!" Dr. Chase said.

Zoe grabbed a sandwich. "Thank you both. We should go. Now"

We hustled out the door and down the stairs, the Chases right behind us.

"Percy," Mrs. Chase called as I was leaving, "tell Annabeth… Tell her she still has a home here, will you? Remind her of that."

I took one last look at the messy living room, Annabeth's half brothers spilling LEGOs and arguing, the smell of cookies filling the air. Not a bad place, I thought.

"I'll tell her," I promised.

We ran out to the yellow VW convertible parked in the driveway. The sun was going down. I figured we had less than an hour to save Annabeth.

"Can't this thing go any faster?" Thalia demanded. Zoe glared at her. "I cannot control traffic."

"You both sound like my mother," I said. "Shut up!" they said in unison.

Zoe weaved in and out of traffic on the Golden Gate Bridge. The sun was sinking on the horizon when we finally got into Marin County and exited the highway.

The roads were insanely narrow, winding through forests and up the sides of hills and around the edges of steep ravines. Zoe didn't slow down at all.

"Why does everything smell like cough drops?" I asked.

"Eucalyptus." Zoe pointed to the huge trees all around us.

"The stuff koala bears eat?"

"And monsters," she said. "They love chewing the leaves. Especially dragons."

"Dragons chew eucalyptus leaves?"

"Believe me," Zoe said, "if you had dragon breath, you would chew eucalyptus too."

I didn't question her, but I did keep my eyes peeled more closely as we drove. Ahead of us loomed Mount Tamalpais. I guess, in terms of mountains, it was a small one, but it looked plenty huge as we were driving toward it.

"So that's the Mountain of Despair?" I asked.

"Yes," Zoe said tightly.

"Why do they call it that?"

She was silent for almost a mile before answering. "After the war between the Titans and the gods, many of the Titans were punished and imprisoned. Kronos was sliced to pieces and thrown into Tartarus. Kronos's right-hand man, the general of his forces, was imprisoned up there, on the summit, just beyond the Garden of the Hesperides."

"The General," I said. Clouds seemed to be swirling around its peak, as though the mountain was drawing them in, spinning them like a top. "What's going on up there? A storm?"

Zoe didn't answer. I got the feeing she knew exactly what the clouds meant, and she didn't like it.

"We have to concentrate," Thalia said. "The Mist is really strong here."

"The magical kind or the natural kind?" I asked.

"Both."

The gray clouds swirled even thicker over the mountain, and we kept driving straight toward them. We were out of the forest now, into wide open spaces of cliffs and grass and rocks and fog.

I happened to glance down at the ocean as we passed a scenic curve, and I saw something that made me jump out of my seat.

"Look!" But we turned a corner and the ocean disappeared behind the hills.

"What?" Thalia asked.

"A big white ship," I said. "Docked near the beach. It looked like a cruise ship."

Her eyes widened. "Luke's ship?"

I wanted to say I wasn't sure. It might be a coincidence. But I knew better. The Princess Andromeda, Luke's demon cruise ship, was docked at that beach. That's why he'd sent his ship all the way down to the Panama Canal. It was the only way to sail it from the East Coast to California.

"We will have company, then," Zoe said grimly. "Kronos's army."

I was about to answer, when suddenly the hairs on the back of my neck stood up. Thalia shouted, "Stop the car. NOW!"

Zoe must've sensed something was wrong, because she slammed on the brakes without question. The yellow VW spun twice before coming to a stop at the edge of the cliff.

"Out!" Thalia opened the door and pushed me hard. We both rolled onto the pavement. The next second: BOOOM!

Lightning flashed, and Dr. Chase's Volkswagen erupted like a canary-yellow grenade. I probably would've been killed by shrapnel except for Thalia's shield, which appeared over me. I heard a sound like metal ram, and when I opened my eyes, we were surrounded by wreckage. Part of the VW's fender had impaled itself in the street. The smoking hood was spinning in circles. Pieces of yellow metal were strewn across the road.