“So then Jason harnessed the venti,” Hazel finished. “And here we are.”

Leo whistled. “Hot-air horses? Dang, Jason. So basically, you held a bunch of gas together all the way to Malta, and then you let it loose.”

Jason frowned. “You know, it doesn’t sound so heroic when you put it that way.”

“Yeah, well. I’m an expert on hot air. I’m still wondering, why Malta? I just kind of ended up here on the raft, but was that a random thing, or—”

“Maybe because of this.” Frank tapped his brochure. “Says here Malta was where Calypso lived.”

A pint of blood drained from Leo’s face. “W-what now?”

Frank shrugged. “According to this, her original home was an island called Gozo just north of here. Calypso’s a Greek myth thingie, right?”

“Ah, a Greek myth thingie!” Coach Hedge rubbed his hands together. “Maybe we get to fight her! Do we get to fight her? ’Cause I’m ready.”

“No,” Leo murmured. “No, we don’t have to fight her, Coach.”

Piper frowned. “Leo, what’s wrong? You look—”

“Nothing’s wrong!” Leo shot to his feet. “Hey, we should get going. We’ve got work to do!”

“But…where did you go?” Hazel asked. “Where did you get those clothes? How—”

“Jeez, ladies!” Leo said. “I appreciate the concern, but I don’t need two extra moms!”

Piper smiled uncertainly. “Okay, but—”

“Ships to fix!” Leo said. “Festus to check! Earth goddesses to punch in the face! What are we waiting for? Leo’s back!”

He spread his arms and grinned.

He was making a brave attempt, but Jason could see the sadness lingering in his eyes. Something had happened to him…something to do with Calypso.

Jason tried to remember the story about her. She was a sorceress of some sort, maybe like Medea or Circe. But if Leo had escaped from an evil sorceress’s lair, why did he seem so sad? Jason would have to talk to him later, make sure his buddy was okay. For now Leo clearly didn’t want to be interrogated.

Jason got up and clapped him on the shoulder. “Leo’s right. We should get going.”

Everybody took the cue. They started wrapping up their food and finishing their drinks.

Suddenly, Hazel gasped. “Guys…”

She pointed to the northeast horizon. At first, Jason saw nothing but the sea. Then a streak of darkness shot into the air like black lightning—as if pure night had torn through the daytime.

“I don’t see anything,” Coach Hedge grumbled.

“Me neither,” Piper said.

Jason scanned his friends’ faces. Most of them just looked confused. Nico was the only other one who seemed to have noticed the black lightning.

“That can’t be…” Nico muttered. “Greece is still hundreds of miles away.”

The darkness flashed again, momentarily leaching the color from the horizon.

“You think it’s Epirus?” Jason’s whole skeleton tingled, the way he felt when he got hit by a thousand volts. He didn’t know why he could see the dark flashes. He wasn’t a child of the Underworld. But it gave him a very bad feeling.

Nico nodded. “The House of Hades is open for business.”

A few seconds later, a rumbling sound washed over them like distant artillery.

“It’s begun,” Hazel said.

“What has?” Leo asked.

When the next flash happened, Hazel’s gold eyes darkened like foil in fire. “Gaea’s final push,” she said. “The Doors of Death are working overtime. Her forces are entering the mortal world en masse.”

“We’ll never make it,” Nico said. “By the time we arrive, there’ll be too many monsters to fight.”

Jason set his jaw. “We’ll defeat them. And we’ll make it there fast. We’ve got Leo back. He’ll give us the speed we need.”

He turned to his friend. “Or is that just hot air?”

Leo managed a crooked grin. His eyes seemed to say: Thanks.

“Time to fly, boys and girls,” he said. “Uncle Leo’s still got a few tricks up his sleeves!”

PERCY WASN’T DEAD YET, but he was already tired of being a corpse.

As they trudged toward the heart of Tartarus, he kept glancing down at his body, wondering how it could belong to him. His arms looked like bleached leather pulled over sticks. His skeletal legs seemed to dissolve into smoke with every step. He’d learned to move normally within the Death Mist, more or less, but the magical shroud still made him feel like he was wrapped in a coat of helium.

He worried that the Death Mist might cling to him forever, even if they somehow managed to survive Tartarus. He didn’t want to spend the rest of his life looking like an extra from The Walking Dead.

Percy tried to focus on something else, but there was no safe direction to look.

Under his feet, the ground glistened a nauseating purple, pulsing with webs of veins. In the dim red light of the blood clouds, Death Mist Annabeth looked like a freshly risen zombie.

Ahead of them was the most depressing view of all.

Spread to the horizon was an army of monsters—flocks of winged arai, tribes of lumbering Cyclopes, clusters of floating evil spirits. Thousands of baddies, maybe tens of thousands, all milling restlessly, pressing against one another, growling and fighting for space—like the locker area of an overcrowded school between classes, if all the students were ’roid-raging mutants who smelled really bad.

Bob led them toward the edge of the army. He made no effort to hide, not that it would have done any good. Being ten feet tall and glowing silver, Bob didn’t do stealth very well.

About thirty yards from the nearest monsters, Bob turned to face Percy.

“Stay quiet and stay behind me,” he advised. “They will not notice you.”

“We hope,” Percy muttered.

On the Titan’s shoulder, Small Bob woke up from a nap. He purred seismically and arched his back, turning skeletal then back to calico. At least he didn’t seem nervous.

Annabeth examined her own zombie hands. “Bob, if we’re invisible…how can you see us? I mean, you’re technically, you know…”

“Yes,” Bob said. “But we are friends.”

“Nyx and her children could see us,” Annabeth said.

Bob shrugged. “That was in Nyx’s realm. That is different.”

“Uh…right.” Annabeth didn’t sound reassured, but they were here now. They didn’t have any choice but to try.

Percy stared at the swarm of vicious monsters. “Well, at least we won’t have to worry about bumping into any other friends in this crowd.”

Bob grinned. “Yes, that is good news! Now, let’s go. Death is close.”

“The Doors of Death are close,” Annabeth corrected. “Let’s watch the phrasing.”

They plunged into the crowd. Percy trembled so badly, he was afraid the Death Mist would shake right off him. He’d seen large groups of monsters before. He’d fought an army of them during the Battle of Manhattan. But this was different.

Whenever he’d fought monsters in the mortal world, Percy at least knew he was defending his home. That gave him courage, no matter how bad the odds were. Here, Percy was the invader. He didn’t belong in this multitude of monsters any more than the Minotaur belonged in Penn Station at rush hour.

A few feet away, a group of empousai tore into the carcass of a gryphon while other gryphons flew around them, squawking in outrage. A six-armed Earthborn and a Laistrygonian giant pummeled each other with rocks, though Percy wasn’t sure if they were fighting or just messing around. A dark wisp of smoke—Percy guessed it must be an eidolon—seeped into a Cyclops, made the monster hit himself in the face, then drifted off to possess another victim.

Annabeth whispered, “Percy, look.”

A stone’s throw away, a guy in a cowboy outfit was cracking a whip at some fire-breathing horses. The wrangler wore a Stetson hat on his greasy hair, an extra-large set of jeans, and a pair of black leather boots. From the side, he might have passed for human—until he turned, and Percy saw that his upper body was split into three different chests, each one dressed in a different-color Western shirt.

It was definitely Geryon, who had tried to kill Percy two years ago in Texas. Apparently the evil rancher was anxious to break in a new herd. The idea of that guy riding out of the Doors of Death made Percy’s sides hurt all over again. His ribs throbbed where the arai had unleashed Geryon’s dying curse back in the forest. He wanted to march up to the three-bodied rancher, smack him in the face, and yell, Thanks a lot, Tex!

Sadly, he couldn’t.

How many other old enemies were in this crowd? Percy began to realize that every battle he’d ever won had only been a temporary victory. No matter how strong or lucky he was, no matter how many monsters he destroyed, Percy would eventually fail. He was only one mortal. He would get too old, too weak, or too slow. He would die. And these monsters…they lasted forever. They just kept coming back. Maybe it would take them months or years to re-form, maybe even centuries. But they would be reborn.

Seeing them assembled in Tartarus, Percy felt as hopeless as the spirits in the River Cocytus. So what if he was a hero? So what if he did something brave? Evil was always here, regenerating, bubbling under the surface. Percy was no more than a minor annoyance to these immortal beings. They just had to outwait him. Someday, Percy’s sons or daughters might have to face them all over again.

Sons and daughters.

The thought jarred him. As quickly as hopelessness had overtaken him, it disappeared. He glanced at Annabeth. She still looked like a misty corpse, but he imagined her true appearance—her gray eyes full of determination, her blond hair pulled back in a bandana, her face weary and streaked with grime, but as beautiful as ever.

Okay, maybe monsters kept coming back forever. But so did demigods. Generation after generation, Camp Half-Blood had endured. And Camp Jupiter. Even separately, the two camps had survived. Now, if the Greeks and Romans could come together, they would be even stronger.

There was still hope. He and Annabeth had come this far. The Doors of Death were almost within reach.

Sons and daughters. A ridiculous thought. An awesome thought. Right there in the middle of Tartarus, Percy grinned.

“What’s wrong?” Annabeth whispered.

With his zombie Death Mist disguise, Percy probably looked like he was grimacing in pain.

“Nothing,” he said. “I was just—”

Somewhere in front of them, a deep voice bellowed: “IAPETUS!”

A TITAN STRODE TOWARD THEM, casually kicking lesser monsters out of his way. He was roughly the same height as Bob, with elaborate Stygian iron armor, a single diamond blazing in the center of his breastplate. His eyes were blue-white, like core samples from a glacier, and just as cold. His hair was the same color, cut military style. A battle helmet shaped like a bear’s head was tucked under his arm. From his belt hung a sword the size of a surfboard.