"We need to go upstream," Zoe said. It was the first time I'd heard her speak since the junkyard, and I was worried about how bad she sounded, like somebody with the flu. "The rapids are too swift."

"Leave that to me," I said. We put the canoes in the water.

Thalia pulled me aside as we were getting the oars. "Thanks for back there."

"Don't mention it."

"Can you really…" She nodded to the rapids. "You know."

"I think so. Usually I'm good with water."

"Would you take Zoe?" she asked. "I think, ah, maybe you can talk to her."

"She's not going to like that."

"Please? I don't know if I can stand being in the same boat with her. She's… she's starting to worry me."

It was about the last thing I wanted to do, but I nodded.

Thalia's shoulders relaxed. "I owe you one."

"Two."

"One and a half," Thalia said.

She smiled, and for a second, I remembered that I actually liked her when she wasn't yelling at me. She turned and helped Grover get their canoe into the water.

As it turned out, I didn't even need to control the currents. As soon as we got in the river, I looked over the edge of the boat and found a couple of naiads staring at me.

They looked like regular teenage girls, the kind you'd see in any mall, except for the fact that they were underwater.

Hey, I said.

They made a bubbling sound that may have been giggling. I wasn't sure. I had a hard time understanding naiads.

We're heading upstream, I told them. Do you think you could—

Before I could even finish, the naiads each chose a canoe and began pushing us up the river. We started so fast

Grover fell into his canoe with his hooves sticking up in the air.

"I hate naiads," Zoe grumbled.

A stream of water squirted up from the back of the boat and hit Zoe in the face.

"She-devils!" Zoe went for her bow.

"Whoa," I said. "They're just playing."

"Cursed water spirits. They've never forgiven me."

"Forgiven you for what?"

She slung her bow back over her shoulder. "It was a long time ago. Never mind."

We sped up the river, the cliffs looming up on either side of us.

"What happened to Bianca wasn't your fault," I told her. "It was my fault. I let her go."

I figured this would give Zoe an excuse to start yelling at me. At least that might shake her out of feeling depressed.

Instead, her shoulders slumped. "No, Percy. I pushed her into going on the quest. I was too anxious. She was a powerful half-blood. She had a kind heart, as well. I… I thought she would be the next lieutenant."

"But you're the lieutenant."

She gripped the strap of her quiver. She looked more tired than I'd ever seen her. "Nothing can last forever, Percy. Over two thousand years I have led the Hunt, and my wisdom has not improved. Now Artemis herself is in danger."

"Look, you can't blame yourself for that."

"If I had insisted on going with her—"

"You think you could've fought something powerful enough to kidnap Artemis? There's nothing you could have done."

Zoe didn't answer.

The cliffs along the river were getting taller. Long shadows fell across the water, making it a lot colder, even though the day was bright.

Without thinking about it, I took Riptide out of my pocket. Zoe looked at the pen, and her expression was pained.

"You made this," I said.

"Who told thee?"

"I had a dream about it."

She studied me. I was sure she was going to call me crazy, but she just sighed. "It was a gift. And a mistake."

"Who was the hero?" I asked.

Zoe shook her head. "Do not make me say his name. I swore never to speak it again."

"You act like I should know him."

"I am sure you do, hero. Don't all you boys want to be just like him?"

Her voice was so bitter, I decided not to ask what she meant. I looked down at Riptide, and for the first time, I wondered if it was cursed.

"Your mother was a water goddess?" I asked.

"Yes, Pleione. She had five daughters. My sisters and I. The Hesperides."

"Those were the girls who lived in a garden at the edge of the West. With the golden apple tree and a dragon guarding it."

"Yes," Zoe said wistfully. "Ladon."

"But weren't there only four sisters'?"

"There are now. I was exiled. Forgotten. Blotted out as if I never existed."

"Why?"

Zoe pointed to my pen. "Because I betrayed my family and helped a hero. You won't find that in the legend either. He never spoke of me. After his direct assault on Ladon failed, I gave him the idea of how to steal the apples, how to trick my father, but he took all the credit."

"But—"

Gurgle, gurgle, the naiad spoke in my mind. The canoe was slowing down.

I looked ahead, and I saw why.

This was as far as they could take us. The river was blocked. A dam the size of a football stadium stood in our path.

"Hoover Dam," Thalia said. "It's huge."

We stood at the river's edge, looking up at a curve of concrete that loomed between the cliffs. People were walking along the top of the dam. They were so tiny they looked like fleas.

The naiads had left with a lot of grumbling—not in words I could understand, but it was obvious they hated this dam blocking up their nice river. Our canoes floated back downstream, swirling in the wake from the dam's discharge vents.

"Seven hundred feet tall," I said. "Built in the 1930s."

"Five million cubic acres of water," Thalia said.

Graver sighed. "Largest construction project in the United States."

Zoe stared at us. "How do you know all that?"

"Annabeth," I said. "She liked architecture."

"She was nuts about monuments," Thalia said.

"Spouted facts all the time." Grover sniffled. "So annoying."

"I wish she were here," I said.

The others nodded. Zoe was still looking at us strangely, but I didn't care. It seemed like cruel fate that we'd come to Hoover Dam, one of Annabeth's personal favorites, and she wasn't here to see it.

"We should go up there," I said. "For her sake. Just to say we've been."

"You are mad," Zoe decided. "But that's where the road is." She pointed to a huge parking garage next to the top of the dam. "And so, sightseeing it is."

We had to walk for almost an hour before we found a path that led up to the road. It came up on the east side of the river. Then we straggled back toward the dam. It was cold and windy on top. On one side, a big lake spread out, ringed by barren desert mountains. On the other side, the dam dropped away like the world's most dangerous skateboard ramp, down to the river seven hundred feet below, and water that churned from the dam's vents.

Thalia walked in the middle of the road, far away from the edges. Grover kept sniffing the wind and looking nervous. He didn't say anything, but I knew he smelled monsters.

"How close are they?" I asked him.

He shook his head. "Maybe not close. The wind on the dam, the desert all around us… the scent can probably carry for miles. But it's coming from several directions. I don't like that."

I didn't either. It was already Wednesday, only two days until winter solstice, and we still had a long way to go. We didn't need any more monsters,

"There's a snack bar in the visitor center," Thalia said.

"You've been here before?" I asked.

"Once. To see the guardians." She pointed to the far end of the dam. Carved into the side of the cliff was a little plaza with two big bronze statues. They looked kind of like Oscar statues with wings.

"They were dedicated to Zeus when the dam was built," Thalia said. "A gift from Athena."

Tourists were clustered all around them. They seemed to be looking at the statues' feet.

"What are they doing?" I asked.

"Rubbing the toes," Thalia said. "They think it's good luck."