“Ah, Grover . . .”

He wiped under his eyes with an oily cloth that left his face grimy, like he had on war paint. “I’m . . . I’m okay.”

But he wasn’t okay. Ever since the encounter in New Mexico—whatever had happened when that wild wind blew through—he seemed really fragile, even more emotional than usual. I was afraid to talk to him about it, because he might start bawling.

At least there’s one good thing about having a friend who gets freaked out more than you do. I realized I couldn’t stay depressed. I had to set aside thinking about Bianca and keep us going forward, the way Thalia was doing. I wondered what she and Zoë were talking about in the front of the truck.

The tow truck ran out of gas at the edge of a river canyon. That was just as well, because the road dead-ended.

Thalia got out and slammed the door. Immediately, one of the tires blew. “Great. What now?”

I scanned the horizon. There wasn’t much to see. Desert in all directions, occasional clumps of barren mountains plopped here and there. The canyon was the only thing interesting. The river itself wasn’t very big, maybe fifty yards across, green water with a few rapids, but it carved a huge scar out of the desert. The rock cliffs dropped away below us.

“There’s a path,” Grover said. “We could get to the river.”

I tried to see what he was talking about, and finally noticed a tiny ledge winding down the cliff face. “That’s a goat path,” I said.

“So?” he asked.

“The rest of us aren’t goats.”

“We can make it,” Grover said. “I think.”

I thought about that. I’d done cliffs before, but I didn’t like them. Then I looked over at Thalia and saw how pale she’d gotten. Her problem with heights . . . she’d never be able to do it.

“No,” I said. “I, uh, think we should go farther upstream.”

Grover said, “But—”

“Come on,” I said. “A walk won’t hurt us.”

I glanced at Thalia. Her eyes said a quick Thank you.

We followed the river about half a mile before coming to an easier slope that led down to the water. On the shore was a canoe rental operation that was closed for the season, but I left a stack of golden drachmas on the counter and a note saying IOU two canoes.

“We need to go upstream,” Zoë 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 Zoë?” 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,” Zoë grumbled.

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

“She-devils!” Zoë 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 Zoë 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.”

Zoë 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. Zoë 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.

Zoë 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,” Zoë 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?”

Zoë 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.

Grover sighed. “Largest construction project in the United States.”

Zoë stared at us. “How do you know all that?”