Percy Jackson & The Olympians: The Demigod Files by Rick Riordan

thief is brave enough to make a deal with her—”
    “He could get back to the world,” Thalia supplied, “and bring the sword to Kronos.”
    “Who would use it to raise his brothers from Tartarus,” I guessed. “And we’d be in big trouble.”
    I struggled to my feet. A wave of nausea almost made me black out, but Thalia grabbed me.
    “Percy,” she said, “you’re in no condition—”
    “I have to be.” I watched as another petal withered and fell off the carnation. Four left before doomsday. “Give me the potted plant. We have to find the cave of Melinoe.”
    As we walked, I tried to think about positive things: my favorite basketball players, my last conversation with Annabeth, what my mom would make for Christmas dinner—anything but the pain. Still, it felt like a saber-toothed tiger was chewing on my shoulder. I wasn’t going to be much good in a fight, and I cursed myself for letting down my guard. I should never have gotten hurt. Now Thalia and Nico would have to haul my useless butt through the rest of the mission.
    I was so busy feeling sorry for myself, I didn’t notice the sound of roaring water until Nico said, “Uh-oh.”
    About fifty feet ahead of us, a dark river churned through a gorge of volcanic rock. I’d seen the Styx, and this didn’t look like the same river. It was narrow and fast. The water was black as ink. Even the foam churned black. The far bank was only thirty feet across, but that was too far to jump, and there was no bridge.
    “The River Lethe.” Nico cursed in Ancient Greek. “We’ll never make it across.”
    The flower was pointing to the other side—toward a gloomy mountain and a path leading up to a cave. Beyond the mountain, the walls of the Underworld loomed like a dark granite sky. I hadn’t considered that the Underworld might have an outer rim, but this appeared to be it.
    “There’s got to be a way across,” I said.
    Thalia knelt next to the bank.
    “Careful!” Nico said. “This is the River of Forgetfulness. If one drop of that water gets on you, you’ll start to forget who you are.”
    Thalia backed up. “I know this place. Luke told me about it once. Souls come here if they choose to be reborn, so they totally forget their former lives.”
    Nico nodded. “Swim in that water and your mind will be wiped clean. You’ll be like a newborn baby.”
    Thalia studied the opposite bank. “I could shoot an arrow across, maybe anchor a line to one of those rocks.”
    “You want to trust your weight to a line that isn’t tied off ?” Nico asked.
    Thalia frowned. “You’re right. Works in the movies, but . . . no. Could you summon some dead people to help us?”
    “I could, but they would only appear on my side of the river. Running water acts as a barrier against the dead. They can’t cross it.”
    I winced. “What kind of stupid rule is that?”
    “Hey, I didn’t make it up.” He studied my face. “You look terrible, Percy. You should sit down.”
    “I can’t. You need me for this.”
    “For what?”Thalia asked. “You can barely stand.”
    “It’s water, isn’t it? I’ll have to control it. Maybe I can redirect the flow long enough to get us across.”
    “In your condition?” Nico said. “No way. I’d feel safer with the arrow idea.”
    I staggered to the edge of the river.
    I didn’t know if I could do this. I was the child of Poseidon, so controlling salt water was no problem. Regular rivers . . . maybe, if the river spirits were feeling cooperative. Magical Underworld rivers? I had no idea.
    “Stand back,” I said.
    I concentrated on the current—the raging black water rushing past. I imagined it was part of my own body. I could control the flow, make it respond to my will.
    I wasn’t sure, but I thought the water churned and bubbled more violently, as if it could sense my presence. I knew I couldn’t stop the river altogether. The current would back up and flood the whole valley, exploding all over us as soon as I let it