He gave Annabeth an embarrassed look, as if realizing he wasn’t helping team morale. “Or maybe she’s badly wounded, and she crawled away to die.”

“Let’s go with that,” Annabeth agreed.

Percy was still shivering. Annabeth wasn’t feeling any warmer either, despite the hot, sticky air. The glass cuts on her hands were still bleeding, which was unusual for her. Normally, she healed fast. Her breathing got more and more labored.

“This place is killing us,” she said. “I mean, it’s literally going to kill us, unless…”

Tartarus. Fire. That distant memory came into focus. She gazed inland toward the cliff, illuminated by flames from below.

It was an absolutely crazy idea. But it might be their only chance.

“Unless what?” Percy prompted. “You’ve got a brilliant plan, haven’t you?”

“It’s a plan,” Annabeth murmured. “I don’t know about brilliant. We need to find the River of Fire.”

WHEN THEY REACHED THE LEDGE, Annabeth was sure she’d signed their death warrants.

The cliff dropped more than eighty feet. At the bottom stretched a nightmarish version of the Grand Canyon: a river of fire cutting a path through a jagged obsidian crevasse, the glowing red current casting horrible shadows across the cliff faces.

Even from the top of the canyon, the heat was intense. The chill of the River Cocytus hadn’t left Annabeth’s bones, but now her face felt raw and sunburned. Every breath took more effort, as if her chest was filled with Styrofoam peanuts. The cuts on her hands bled more rather than less. Annabeth’s foot, which had been almost healed, seemed to be reinjuring itself. She’d taken off her makeshift cast, but now she regretted it. Each step made her wince.

Assuming they could make it down to the fiery river, which she doubted, her plan seemed certifiably insane.

“Uh…” Percy examined the cliff. He pointed to a tiny fissure running diagonally from the edge to the bottom. “We can try that ledge there. Might be able to climb down.”

He didn’t say they’d be crazy to try. He managed to sound hopeful. Annabeth was grateful for that, but she also worried that she was leading him to his doom.

Of course if they stayed here, they would die anyway. Blisters had started to form on their arms from exposure to the Tartarus air. The whole environment was about as healthy as a nuclear blast zone.

Percy went first. The ledge was barely wide enough to allow a toehold. Their hands clawed for any crack in the glassy rock. Every time Annabeth put pressure on her bad foot, she wanted to yelp. She’d ripped off the sleeves of her T-shirt and used the cloth to wrap her bloody palms, but her fingers were still slippery and weak.

A few steps below her, Percy grunted as he reached for another handhold. “So…what is this fire river called?”

“The Phlegethon,” she said. “You should concentrate on going down.”

“The Phlegethon?” He shinnied along the ledge. They’d made it roughly a third of the way down the cliff—still high enough up to die if they fell. “Sounds like a marathon for hawking spitballs.”

“Please don’t make me laugh,” she said.

“Just trying to keep things light.”

“Thanks,” she grunted, nearly missing the ledge with her bad foot. “I’ll have a smile on my face as I plummet to my death.”

They kept going, one step at a time. Annabeth’s eyes stung with sweat. Her arms trembled. But to her amazement, they finally made it to the bottom of the cliff.

When she reached the ground, she stumbled. Percy caught her. She was alarmed by how feverish his skin felt. Red boils had erupted on his face, so he looked like a smallpox victim.

Her own vision was blurry. Her throat felt blistered, and her stomach was clenched tighter than a fist.

We have to hurry, she thought.

“Just to the river,” she told Percy, trying to keep the panic out of her voice. “We can do this.”

They staggered over slick glass ledges, around massive boulders, avoiding stalagmites that would’ve impaled them with any slip of the foot. Their tattered clothes steamed from the heat of the river, but they kept going until they crumpled to their knees at the banks of the Phlegethon.

“We have to drink,” Annabeth said.

Percy swayed, his eyes half-closed. It took him a three-count to respond. “Uh…drink fire?”

“The Phlegethon flows from Hades’s realm down into Tartarus.” Annabeth could barely talk. Her throat was closing up from the heat and the acidic air. “The river is used to punish the wicked. But also…some legends call it the River of Healing.”

“Some legends?”

Annabeth swallowed, trying to stay conscious. “The Phlegethon keeps the wicked in one piece so that they can endure the torments of the Fields of Punishment. I think…it might be the Underworld equivalent of ambrosia and nectar.”

Percy winced as cinders sprayed from the river, curling around his face. “But it’s fire. How can we—”

“Like this.” Annabeth thrust her hands into the river.

Stupid? Yes, but she was convinced they had no choice. If they waited any longer, they would pass out and die. Better to try something foolish and hope it worked.

On first contact, the fire wasn’t painful. It felt cold, which probably meant it was so hot it was overloading Annabeth’s nerves. Before she could change her mind, she cupped the fiery liquid in her palms and raised it to her mouth.

She expected a taste like gasoline. It was so much worse. Once, at a restaurant back in San Francisco, she’d made the mistake of tasting a ghost chili pepper that came with a plate of Indian food. After barely nibbling it, she thought her respiratory system was going to implode. Drinking from the Phlegethon was like gulping down a ghost chili smoothie. Her sinuses filled with liquid flame. Her mouth felt like it was being deep-fried. Her eyes shed boiling tears, and every pore on her face popped. She collapsed, gagging and retching, her whole body shaking violently.

“Annabeth!” Percy grabbed her arms and just managed to stop her from rolling into the river.

The convulsions passed. She took a ragged breath and managed to sit up. She felt horribly weak and nauseous, but her next breath came more easily. The blisters on her arms were starting to fade.

“It worked,” she croaked. “Percy, you’ve got to drink.”

“I…” His eyes rolled up in his head, and he slumped against her.

Desperately, she cupped more fire in her palm. Ignoring the pain, she dripped the liquid into Percy’s mouth. He didn’t respond.

She tried again, pouring a whole handful down his throat. This time he spluttered and coughed. Annabeth held him as he trembled, the magical fire coursing through his system. His fever disappeared. His boils faded. He managed to sit up and smack his lips.

“Ugh,” he said. “Spicy, yet disgusting.”

Annabeth laughed weakly. She was so relieved, she felt light-headed. “Yeah. That pretty much sums it up.”

“You saved us.”

“For now,” she said. “The problem is, we’re still in Tartarus.”

Percy blinked. He looked around as if just coming to terms with where they were. “Holy Hera. I never thought…well, I’m not sure what I thought. Maybe that Tartarus was empty space, a pit with no bottom. But this is a real place.”

Annabeth recalled the landscape she’d seen while they fell—a series of plateaus leading ever downward into the gloom.

“We haven’t seen all of it,” she warned. “This could be just the first tiny part of the abyss, like the front steps.”

“The welcome mat,” Percy muttered.

They both gazed up at the blood-colored clouds swirling in the gray haze. No way would they have the strength to climb back up that cliff, even if they wanted to. Now there were only two choices: downriver or upriver, skirting the banks of the Phlegethon.

“We’ll find a way out,” Percy said. “The Doors of Death.”

Annabeth shuddered. She remembered what Percy had said just before they fell into Tartarus. He’d made Nico di Angelo promise to lead the Argo II to Epirus, to the mortal side of the Doors of Death.

We’ll see you there, Percy had said.

That idea seemed even crazier than drinking fire. How could the two of them wander through Tartarus and find the Doors of Death? They’d barely been able to stumble a hundred yards in this poisonous place without dying.

“We have to,” Percy said. “Not just for us. For everybody we love. The Doors have to be closed on both sides, or the monsters will just keep coming through. Gaea’s forces will overrun the world.”

Annabeth knew he was right. Still…when she tried to imagine a plan that could succeed, the logistics overwhelmed her. They had no way of locating the Doors. They didn’t know how much time it would take, or even if time flowed at the same speed in Tartarus. How could they possibly synchronize a meeting with their friends? And Nico had mentioned a legion of Gaea’s strongest monsters guarding the Doors on the Tartarus side. Annabeth and Percy couldn’t exactly launch a frontal assault.

She decided not to mention any of that. They both knew the odds were bad. Besides, after swimming in the River Cocytus, Annabeth had heard enough whining and moaning to last a lifetime. She promised herself never to complain again.

“Well.” She took a deep breath, grateful at least that her lungs didn’t hurt. “If we stay close to the river, we’ll have a way to heal ourselves. If we go downstream—”

It happened so fast, Annabeth would have been dead if she’d been on her own.

Percy’s eyes locked on something behind her. Annabeth spun as a massive dark shape hurtled down at her—a snarling, monstrous blob with spindly barbed legs and glinting eyes.

She had time to think: Arachne. But she was frozen in terror, her senses smothered by the sickly sweet smell.

Then she heard the familiar SHINK of Percy’s ballpoint pen transforming into a sword. His blade swept over her head in a glowing bronze arc. A horrible wail echoed through the canyon.

Annabeth stood there, stunned, as yellow dust—the remains of Arachne—rained around her like tree pollen.

“You okay?” Percy scanned the cliffs and boulders, alert for more monsters, but nothing else appeared. The golden dust of the spider settled on the obsidian rocks.

Annabeth stared at her boyfriend in amazement. Riptide’s Celestial bronze blade glowed even brighter in the gloom of Tartarus. As it passed through the thick hot air, it made a defiant hiss like a riled snake.

“She…she would’ve killed me,” Annabeth stammered.

Percy kicked the dust on the rocks, his expression grim and dissatisfied. “She died too easily, considering how much torture she put you through. She deserved worse.”

Annabeth couldn’t argue with that, but the hard edge in Percy’s voice made her unsettled. She’d never seen someone get so angry or vengeful on her behalf. It almost made her glad Arachne had died quickly. “How did you move so fast?”

Percy shrugged. “Gotta watch each other’s backs, right? Now, you were saying…downstream?”