But the sky stayed gray and snowy. No sign of a helpful thunderstorm.

"There!" Bianca said. "That parking lot!"

"We'll be trapped," Zoe said.

"Trust me," Bianca said.

Zoe shot across two lanes of traffic and into a mall parking lot on the south bank of the river. We left the van and followed Bianca down some steps.

"Subway entrance," Bianca said. "Let's go south. Alexandria."

"Anything," Thalia agreed.

We bought tickets and got through the turnstiles, looking behind us for any signs of pursuit. A few minutes later we were safely aboard a southbound train, riding away from D.C. As our train came above ground, we could see the helicopter circling the parking lot, but it didn't come after us.

Grover let out a sigh. "Nice job, Bianca, thinking of the subway."

Bianca looked pleased. "Yeah, well. I saw that station when Nico and I came through last summer. I remember being really surprised to see it, because it wasn't here when we used to live in D.C."

Grover frowned. "New? But that station looked really old."

"I guess," Bianca said. "But trust me, when we lived here as little kids, there was no subway."

Thalia sat forward. "Wait a minute. No subway at all?"

Bianca nodded.

Now, I knew nothing about D.C., but I didn't see how their whole subway system could be less than twelve years old. I guess everyone else was thinking the same thing, because they looked pretty confused.

"Bianca," Zoe said. "How long ago…" Her voice faltered. The sound of the helicopter was getting louder again.

"We need to change trains," I said. "Next station."

Over the next half hour, all we thought about was getting away safely. We changed trains twice. I had no idea where we were going, but after a while we lost the helicopter.

Unfortunately, when we finally got off the train we found ourselves at the end of the line, in an industrial area with nothing but warehouses and railway tracks. And snow. Lots of snow. It seemed much colder here. I was glad for my new lion's fur coat.

We wandered through the railway yard, thinking there might be another passenger train somewhere, but there were just rows and rows of freight cars, most of which were covered in snow, like they hadn't moved in years.

A homeless guy was standing at a trash-can fire. We must've looked pretty pathetic, because he gave us a toothless grin and said, "Y'all need to get warmed up? Come on over!

We huddled around his fire, Thalia's teeth were chattering. She said, "Well this is g-g-g-great."

"My hooves are frozen," Grover complained.

"Feet," I corrected, for the sake of the homeless guy.

"Maybe we should contact camp," Bianca said. "Chiron—"

"No," Zoe said. "They cannot help us anymore. We must finish this quest ourselves."

I gazed miserably around the rail yard. Somewhere, far to the west, Annabeth was in danger. Artemis was in chains. A doomsday monster was on the loose. And we were stuck on the outskirts of D.C., sharing a homeless persons fire.

"You know," the homeless man said, "you're never completely without friends." His face was grimy and his beard tangled, but his expression seemed kindly. "You kids need a train going west?"

"Yes, sir," I said. "You know of any?"

He pointed one greasy hand.

Suddenly I noticed a freight train, gleaming and free of snow. It was one of those automobile-carrier trains, with steel mesh curtains and a triple-deck of cars inside. The side of the freight train said SUN WEST LINE.

"That's… convenient," Thalia said. "Thanks, uh…"

She turned to the homeless guy, but he was gone. The trash can in front of us was cold and empty, as if he'd taken the flames with him.

An hour later we were rumbling west. There was no problem about who would drive now, because we all got our own luxury car. Zoe and Bianca were crashed out in a Lexus on the top deck. Grover was playing race car driver behind the wheel of a Lamborghini. And Thalia had hot-wired the radio in a black Mercedes SLK so she could pick up the alt-rock stations from D.C.

"Join you?" I asked her.

She shrugged, so I climbed into the shotgun seat.

The radio was playing the White Stripes. I knew the song because it was one of the only CDs I owned that my mom liked. She said it reminded her of Led Zeppelin. Thinking about my mom made me sad, because it didn't seem likely I'd be home for Christmas. I might not live that long.

"Nice coat," Thalia told me.

I pulled the brown duster around me, thankful for the warmth. "Yeah, but the Nemean Lion wasn't the monster we're looking for."

"Not even close. We've got a long way to go."

"Whatever this mystery monster is, the General said it would come for you. They wanted to isolate you from the group, so the monster will appear and battle you one-on-one."

"He said that?"

"Well, something like that. Yeah."

"That's great. I love being used as bait."

"No idea what the monster might be?"

She shook her head morosely. "But you know where we're going, don't you? San Francisco. That's where Artemis was heading."

I remembered something Annabeth had said at the dance: how her dad was moving to San Francisco, and there was no way she could go. Half-bloods couldn't live there.

"Why?" I asked. "What's so bad about San Francisco?"

"The Mist is really thick there because the Mountain of Despair is so near. Titan magic—what's left of it—still lingers. Monsters are attracted to that area like you wouldn't believe."

"What's the Mountain of Despair?"

Thalia raised an eyebrow. "You really don't know? Ask stupid Zoe. She's the expert."

She glared out the windshield. I wanted to ask her what she was talking about, but I also didn't want to sound like an idiot. I hated feeling like Thalia knew more than I did, so I kept my mouth shut.

The afternoon sun shone through the steel-mesh side of the freight car, casting a shadow across Thalia's face. I thought about how different she was from Zoe—Zoe all formal and aloof like a princess, Thalia with her ratty clothes and her rebel attitude. But there was something similar about them, too. The same kind of toughness. Right now, sitting in the shadows with a gloomy expression, Thalia looked a lot like one of the Hunters.

Then suddenly, it hit me: "That's why you don't get along with Zoe."

Thalia frowned. "What?"

"The Hunters tried to recruit you," I guessed.

Her eyes got dangerously bright. I thought she was going to zap me out of the Mercedes, but she just sighed. I almost joined them," she admitted. "Luke, Annabeth, and I ran into them once, and Zoe tried to convince me. She almost did, but…"

"But?"

Thalia's fingers gripped the wheel. "I would've had to leave Luke."

"Oh."

"Zoe and I got into a fight. She told me I was being stupid. She said I'd regret my choice. She said Luke would let me down someday."

I watched the sun through the metal curtain. We seemed to be traveling faster each second—shadows flickering like an old movie projector.

"That's harsh," I said. "Hard to admit Zoe was right."

"She wasn't right! Luke never let me down. Never."

"We'll have to fight him," I said. "There's no way around it."

Thalia didn't answer.

"You haven't seen him lately," I warned. "I know it's hard to believe, but—"

"I'll do what I have to."

"Even if that means killing him?"

"Do me a favor," she said. "Get out of my car."

I felt so bad for her I didn't argue.

As I was about to leave, she said, "Percy."

When I looked back, her eyes were red, but I couldn't tell if it was from anger or sadness. "Annabeth wanted to join the Hunters, too. Maybe you should think about why."

Before I could respond, she raised the power windows and shut me out.