If you can picture that, you have a pretty good idea what the Fields of Asphodel looked like. The black grass had been trampled by eons of dead feet. A warm, moist wind blew like the breath of a swamp. Black trees—Grover told me they were poplars—grew in clumps here and there.

The cavern ceiling was so high above us it might've been a bank of storm clouds, except for the stalactites, which glowed faint gray and looked wickedly pointed. I tried not to imagine they'd fall on us at any moment, but dotted around the fields were several that had fallen and impaled themselves in the black grass. I guess the dead didn't have to worry about little hazards like being speared by stalactites the size of booster rockets.

Annabeth, Grover, and I tried to blend into the crowd, keeping an eye out for security ghouls. I couldn't help looking for familiar faces among the spirits of Asphodel, but the dead are hard to look at. Their faces shimmer. They all look slightly angry or confused. They will come up to you and speak, but their voices sound like chatter, like bats twittering. Once they realize you can't understand them, they frown and move away.

The dead aren't scary. They're just sad.

We crept along, following the line of new arrivals that snaked from the main gates toward a black-tented pavilion with a banner that read:

JUDGMENTS FOR ELYSIUM AND ETERNAL DAMNATION

Welcome, Newly Deceased!

Out the back of the tent came two much smaller lines.

To the left, spirits flanked by security ghouls were marched down a rocky path toward the Fields of Punishment, which glowed and smoked in the distance, a vast, cracked wasteland with rivers of lava and minefields and miles of barbed wire separating the different torture areas. Even from far away, I could see people being chased by hellhounds, burned at the stake, forced to run naked through cactus patches or listen to opera music. I could just make out a tiny hill, with the ant-size figure of Sisyphus struggling to move his boulder to the top. And I saw worse tortures, too—things I don't want to describe.

The line coming from the right side of the judgment pavilion was much better. This one led down toward a small valley surrounded by walls—a gated community, which seemed to be the only happy part of the Underworld. Beyond the security gate were neighborhoods of beautiful houses from every time period in history, Roman villas and medieval castles and Victorian mansions. Silver and gold flowers bloomed on the lawns. The grass rippled in rainbow colors. I could hear laughter and smell barbecue cooking.

Elysium.

In the middle of that valley was a glittering blue lake, with three small islands like a vacation resort in the Bahamas. The Isles of the Blest, for people who had chosen to be reborn three times, and three times achieved Elysium. Immediately I knew that's where I wanted to go when I died.

"That's what it's all about," Annabeth said, like she was reading my thoughts. "That's the place for heroes."

But I thought of how few people there were in Elysium, how tiny it was compared to the Fields of Asphodel or even the Fields of Punishment. So few people did good in their lives. It was depressing.

We left the judgment pavilion and moved deeper into the Asphodel Fields. It got darker. The colors faded from our clothes. The crowds of chattering spirits began to thin.

After a few miles of walking, we began to hear a familiar screech in the distance. Looming on the horizon was a palace of glittering black obsidian. Above the parapets swirled three dark batlike creatures: the Furies. I got the feeling they were waiting for us.

"I suppose it's too late to turn back," Grover said wistfully.

"We'll be okay." I tried to sound confident.

"Maybe we should search some of the other places first," Grover suggested. "Like, Elysium, for instance ..."

"Come on, goat boy." Annabeth grabbed his arm.

Grover yelped. His sneakers sprouted wings and his legs shot forward, pulling him away from Annabeth. He landed flat on his back in the grass.

"Grover," Annabeth chided. "Stop messing around."

"But I didn't—"

He yelped again. His shoes were flapping like crazy now. They levitated off the ground and started dragging him away from us.

"Maia!" he yelled, but the magic word seemed to have no effect. "Maia, already! Nine-one-one! Help!"

I got over being stunned and made a grab for Grover's hand, but too late. He was picking up speed, skidding downhill like a bobsled.

We ran after him.

Annabeth shouted, "Untie the shoes!"

It was a smart idea, but I guess it's not so easy when your shoes are pulling you along feetfirst at full speed. Grover tried to sit up, but he couldn't get close to the laces.

We kept after him, trying to keep him in sight as he ripped between the legs of spirits who chattered at him in annoyance.

I was sure Grover was going to barrel straight through the gates of Hades's palace, but his shoes veered sharply to the right and dragged him in the opposite direction.

The slope got steeper. Grover picked up speed. Annabeth and I had to sprint to keep up. The cavern walls narrowed on either side, and I realized we'd entered some kind of side tunnel. No black grass or trees now, just rock underfoot, and the dim light of the stalactites above.

"Grover!" I yelled, my voice echoing. "Hold on to something!"

"What?" he yelled back.

He was grabbing at gravel, but there was nothing big enough to slow him down.

The tunnel got darker and colder. The hairs on my arms bristled. It smelled evil down here. It made me think of things I shouldn't even know about—blood spilled on an ancient stone altar, the foul breath of a murderer.

Then I saw what was ahead of us, and I stopped dead in my tracks.

The tunnel widened into a huge dark cavern, and in the middle was a chasm the size of a city block.

Grover was sliding straight toward the edge.

"Come on, Percy!" Annabeth yelled, tugging at my wrist.

"But that's—"

"I know!" she shouted. "The place you described in your dream! But Grover's going to fall if we don't catch him." She was right, of course. Grover's predicament got me moving again.

He was yelling, clawing at the ground, but the winged shoes kept dragging him toward the pit, and it didn't look like we could possibly get to him in time.

What saved him were his hooves.

The flying sneakers had always been a loose fit on him, and finally Grover hit a big rock and the left shoe came flying off. It sped into the darkness, down into the chasm. The right shoe kept tugging him along, but not as fast. Grover was able to slow himself down by grabbing on to the big rock and using it like an anchor.

He was ten feet from the edge of the pit when we caught him and hauled him back up the slope. The other winged shoe tugged itself off, circled around us angrily and kicked our heads in protest before flying off into the chasm to join its twin.

We all collapsed, exhausted, on the obsidian gravel. My limbs felt like lead. Even my backpack seemed heavier, as if somebody had filled it with rocks.

Grover was scratched up pretty bad. His hands were bleeding. His eyes had gone slit-pupiled, goat style, the way they did whenever he was terrified.

"I don't know how ..." he panted. "I didn't..."

"Wait," I said. "Listen."

I heard something—a deep whisper in the darkness.

Another few seconds, and Annabeth said, "Percy, this place—"

"Shh." I stood.

The sound was getting louder, a muttering, evil voice from far, far below us. Coming from the pit.

Grover sat up. "Wh—what's that noise?"

Annabeth heard it too, now. I could see it in her eyes. "Tartarus. The entrance to Tartarus." I uncapped Anaklusmos.

The bronze sword expanded, gleaming in the darkness, and the evil voice seemed to falter, just for a moment, before resuming its chant.

I could almost make out words now, ancient, ancient words, older even than Greek. As if ...

"Magic," I said.

"We have to get out of here," Annabeth said.

Together, we dragged Grover to his hooves and started back up the tunnel. My legs wouldn't move fast enough. My backpack weighed me down. The voice got louder and angrier behind us, and we broke into a run.

Not a moment too soon.

A cold blast of wind pulled at our backs, as if the entire pit were inhaling. For a terrifying moment, I lost ground, my feet slipping in the gravel. If we'd been any closer to the edge, we would've been sucked in.

We kept struggling forward, and finally reached the top of the tunnel, where the cavern widened out into the Fields of Asphodel. The wind died. A wail of outrage echoed from deep in the tunnel. Something was not happy we'd gotten away.

"What was that?" Grover panted, when we'd collapsed in the relative safety of a black poplar grove. "One of Hades's pets?"

Annabeth and I looked at each other. I could tell she was nursing an idea, probably the same one she'd gotten during the taxi ride to L.A., but she was too scared to share it. That was enough to terrify me.

I capped my sword, put the pen back in my pocket. "Let's keep going." I looked at Grover. "Can you walk?"

He swallowed. "Yeah, sure. I never liked those shoes, anyway."

He tried to sound brave about it, but he was trembling as badly as Annabeth and I were. Whatever was in that pit was nobody's pet. It was unspeakably old and powerful. Even Echidna hadn't given me that feeling. I was almost relieved to turn my back on that tunnel and head toward the palace of Hades.

Almost.

The Furies circled the parapets, high in the gloom. The outer walls of the fortress glittered black, and the two-story-tall bronze gates stood wide open.

Up close, I saw that the engravings on the gates were scenes of death. Some were from modern times—an atomic bomb exploding over a city, a trench filled with gas mask-wearing soldiers, a line of African famine victims waiting with empty bowls—but all of them looked as if they'd been etched into the bronze thousands of years ago. I wondered if I was looking at prophecies that had come true.

Inside the courtyard was the strangest garden I'd ever seen. Multicolored mushrooms, poisonous shrubs, and weird luminous plants grew without sunlight. Precious jewels made up for the lack of flowers, piles of rubies as big as my fist, clumps of raw diamonds. Standing here and there like frozen party guests were Medusa's garden statues— petrified children, satyrs, and centaurs—all smiling grotesquely.

In the center of the garden was an orchard of pomegranate trees, their orange blooms neon bright in the dark. "The garden of Persephone," Annabeth said. "Keep walking."

I understood why she wanted to move on. The tart smell of those pomegranates was almost overwhelming. I had a sudden desire to eat them, but then I remembered the story of Persephone. One bite of Underworld food, and we would never be able to leave. I pulled Grover away to keep him from picking a big juicy one.

We walked up the steps of the palace, between black columns, through a black marble portico, and into the house of Hades. The entry hall had a polished bronze floor, which seemed to boil in the reflected torchlight. There was no ceiling, just the cavern roof, far above. I guess they never had to worry about rain down here.

Every side doorway was guarded by a skeleton in military gear. Some wore Greek armor, some British redcoat uniforms, some camouflage with tattered American flags on the shoulders. They carried spears or muskets or M-16s. None of them bothered us, but their hollow eye sockets followed us as we walked down the hall, toward the big set of doors at the opposite end.