THE BOAT CAPTAINS in Seward had warned Brooklyn it was three hundred nautical miles to the Hubbard Glacier, a hard, dangerous journey, but Arion had no trouble. He raced over the water at the speed of sound, heating the air around them so that she didn't even feel the cold.

That was the only good thing about this, though. She was holding on for dear life, and she promised herself that she would never do this ever again. Fuck everything; she'd make them leave her in Alaska if they had to get back using this horse.

They raced through icy straits, past blue fjords and cliffs with waterfalls spilling into the sea. Arion jumped over a breaching humpback whale and kept galloping, startling a pack of seals off an iceberg.

It seemed like only minutes before they zipped into a narrow bay. The water turned into the consistency of shaved ice in blue sticky syrup. Arion came to a halt on a frozen turquoise slab.

A half a mile away stood Hubbard Glacier. Brooklyn couldn't quite process what she was looking at. Purple snowcapped mountains marched off in either direction, with clouds floating around their middles like fluffy belts. In a massive valley between two of the largest peaks, a ragged wall of ice rose out of the sea, filling the entire gorge. The glacier was blue and white with streaks of black, so that it looked like a hedge of dirty snow left behind on a sidewalk after a snowplow had gone by, only four million times as large.

As soon as Arion stopped, Brooklyn felt the temperature drop. All that ice was sending off waves of cold, turning the bay into the world's largest refrigerator. The eeriest thing was a sound like thunder that rolled across the water.

"What is that?" Frank gazed at the clouds above the glacier. "A storm?"

"No," Hazel said. "Ice cracking and shifting. Millions of tons of ice."

"You mean that thing is breaking up?" Brooklyn asked.

As if on cue, a sheet of ice silently calved off the side of the glacier and crashed into the sea, spraying water and frozen shrapnel several stories high. A millisecond later the sound hit them — a BOOM almost as jarring as Arion hitting the sound barrier.

"We can't get close to that thing!" Frank said.

"We have to," Percy said. "The giant is at the top."

Arion nickered.

"Jeez, Hazel," Percy said, "tell your horse to watch his language."

Hazel let out a small laugh. "What did he say?"

"With the cussing removed? He said he can get us to the top."

Frank looked incredulous. "I thought the horse couldn't fly!"

This time Arion whinnied so angrily, Brooklyn could guess he was cursing.

"Dude," Percy told the horse, "I've gotten suspended for saying less than that. Hazel, he promises you'll see what he can do as soon as you give the word."

"Um, hold on, then, you guys," Hazel said nervously. "Arion, giddyup!"

Arion shot toward the glacier like a runaway rocket, barreling straight across the slush like he wanted to play chicken with the mountain of ice.

The air grew colder. The crackling of the ice grew louder. As Arion closed the distance, the glacier loomed so large, Brooklyn got vertigo just trying to take it all in. The side was riddled with crevices and caves, spiked with jagged ridges like ax blades. Pieces were constantly crumbling off — some no larger than snowballs, some the size of houses.

When they were about fifty yards from the base, a thunderclap rattled Brooklyn's bones, and a curtain of ice that would have covered Camp Jupiter calved away and fell toward them.

"Look out!" Frank shouted, which seemed a little unnecessary to her.

Arion was way ahead of him. In a burst of speed, he zigzagged through the debris, leaping over chunks of ice and clambering up the face of the glacier.

Brooklyn, Percy, and Frank cussed like horses and held on desperately while Hazel wrapped her arms around Arion's neck. Somehow, they managed not to fall off as Arion scaled the cliffs, jumping from foothold to foothold with impossible speed and agility. It was like falling down a mountain in reverse.

Then it was over. The horse stood proudly at the top of a ridge of ice that loomed over the void. The sea was now three hundred feet below them.

He whinnied a challenge that echoed off the mountains. Percy didn't translate, but Brooklyn was pretty sure Arion was calling out to any other horses that might be in the bay: Beat that, ya punks!

Then he turned and ran inland across the top of the glacier, leaping a chasm fifty feet across.

"There!" Percy pointed.

The horse stopped. Ahead of them stood a frozen Roman camp like a giant-sized ghastly replica of Camp Jupiter. The trenches bristled with ice spikes. The snow-brick ramparts glared blinding white. Hanging from the guard towers, banners of frozen blue cloth shimmered in the arctic sun.

There was no sign of life. The gates stood wide open. No sentries walked the walls. Still, Brooklyn had an uneasy feeling in her gut. This place felt weird, as if the earth were trying to wake up and consume everything — as if the mountains on either side wanted to crush them and the entire glacier to pieces.

Arion trotted skittishly.

"Brooks, Frank," Percy said, "how about we go on foot from here?"

"If you weren't going to say it, I was going to jump down," Brooklyn sighed with relief.

They dismounted and took some tentative steps. The ice seemed stable, covered with a fine carpet of snow so that it wasn't too slippery. Thank the gods she wasn't wearing her heels.

Hazel urged Arion forward. Percy, Frank, and Brooklyn walked close by, weapons ready. They approached the gates without being challenged. Brooklyn saw nothing — just the yawning icy gates and the frozen banners crackling in the wind.

She could see straight down the Via Praetoria. At the crossroads, in front of the snow-brick principia, a tall, dark-robed figure stood, bound in icy chains.

"Thanatos," Hazel murmured.

Her eyes fluttered. She almost fell off Arion, but Frank caught her and propped her up.

"We've got you," he promised. "Nobody's taking you away."

Hazel gripped his hand. "I'm all right," she said, but she was totally lying.

Percy looked around uneasily. "No defenders? No giant? This has to be a trap."

"Obviously," Brooklyn said. "But I don't think we have a choice."

Hazel urged Arion through the gates. The layout was so familiar — cohort barracks, baths, armory. It was an exact replica of Camp Jupiter, except three times as big. Brooklyn felt tiny and insignificant, as if they were moving through a model city constructed by the gods. She remembered that feeling, at the very least, but she didn't like it.

They stopped ten feet from the robed figure.

"Hello?" Hazel asked quietly. "Mr. Death?"

The hooded figure raised his head.

Instantly, the whole camp stirred to life. Figures in Roman armor emerged from the barracks, the principia, the armory, and the canteen, but they weren't human. Their bodies weren't much more than wisps of black vapor, but they managed to hold together sets of scale armor, greaves, and helmets. Frost-covered swords were strapped to their waists. Pila and dented shields floated in their smoky hands. The plumes on the centurions' helmets were frozen and ragged. Most of the figures — shades, Brooklyn's mind finally supplied, Jesus Christ — were on foot, but two soldiers burst out of the stables in a golden chariot pulled by ghostly black steeds.

When Arion saw the horses, he stamped the ground in outrage.

Frank gripped his bow. "Yep, here's the trap."

* * *

The ghosts formed ranks and encircled the crossroads. There were about a hundred in all — not an entire legion, but more than a cohort. Some carried the tattered lightning bolt banners of the Twelfth Legion, Fifth Cohort — Michael Varus's doomed expedition from the 1980s. Others carried standards and insignia Brooklyn faintly recognized, as if they'd died at different times, on different quests — not even from Camp Jupiter. Most were armed with Imperial gold weapons.

"Thanatos!" Hazel turned to the robed figure. "We're here to rescue you. If you control these shades, tell them—"

Her voice faltered. The god's hood fell away and his robes dropped off as he spread his wings, leaving him in only a sleeveless black tunic belted at the waist. He was one of the most beautiful men Brooklyn had ever seen.

His skin was the color of teakwood, dark and glistening. His eyes were as honey gold as Hazel's. He was lean and muscular, with a regal face and black hair flowing down his shoulders. His wings glimmered in shades of blue, black, and purple.

Brooklyn reminded herself to breathe.

Beautiful was the right word for Thanatos — not handsome, or hot, or anything like that. He was beautiful the way an angel is beautiful — timeless, perfect, remote.

"Oh," Hazel said in a small voice.

The god's wrists were shackled in icy manacles, with chains that ran straight into the glacier floor. His feet were bare, shackled around the ankles and also chained.

"It's Cupid," Frank said.

"A really buff Cupid," Brooklyn agreed.

"You compliment me," Thanatos said. His voice was as gorgeous as he was — deep and melodious. "I am frequently mistaken for the god of love. Death has more in common with Love than you might imagine. But I am Death. I assure you."

Brooklyn didn't doubt it. She felt as if she were made of ashes. Any second, she might crumble and be sucked into the vacuum. She doubted Thanatos even needed to touch her to kill her. He could simply tell her to die. She would keel over on the spot, her soul obeying that beautiful voice and those kind eyes.

"We're — we're here to save you," Hazel said quietly. "Where's Alcyoneus?"

"Save me . . ." Thanatos narrowed his eyes. "Do you understand what you are saying, Hazel Levesque? Do you understand what that will mean?"

Percy stepped forward. "We're wasting time."

He swung his sword at the god's chains. Celestial bronze rang against the ice, but Riptide stuck to the chain like glue. Frost began creeping up the blade. Percy pulled frantically. Brooklyn and Frank ran to help. Together, they just managed to yank Riptide free before the frost reached their hands.

"That won't work," Thanatos said simply. "As for the giant, he is close. These shades are not mine. They are his."

His eyes scanned the ghost soldiers. They shifted uncomfortably, as if an arctic wind were rattling through their ranks.

"So how do we get you out?" Hazel demanded.

Thanatos turned his attention back to her. "Daughter of Pluto, child of my master, you of all people should not wish me released."

"Don't you think I know that?" she demanded. "Listen, Death." She drew her cavalry sword, and Arion reared in defiance. "I didn't come back from the Underworld and travel thousands of miles to be told that I'm stupid for setting you free. If I die, I die. I'll fight this whole army if I have to. Just tell us how to break your chains."

Thanatos studied her for a heartbeat. "Interesting. You do understand that these shades were once demigods like you. They fought for Rome. They died without completing their heroic quests. Like you, they were sent to Asphodel. Now Gaea has promised them a second life if they fight for her today. Of course, if you release me and defeat them, they will have to return to the Underworld where they belong. For treason against the gods, they will face eternal punishment. They are not so different from you, Hazel Levesque. Are you sure you want to release me and damn these souls forever?"

Frank clenched his fists. "That's not fair! Do you want to be freed or not?"

"Fair . . ." Death mused. "You'd be amazed how often I hear that word, Frank Zhang, and how meaningless it is. Is it fair that your life will burn so short and bright? Was it fair when I guided your mother to the Underworld?"

Frank staggered like he'd been punched.

"No," Death said sadly. "Not fair. And yet it was her time. There is no fairness in Death. If you free me, I will do my duty. But of course these shades will try to stop you."

"So if we let you go," Brooklyn summed up, "we get mobbed by a bunch of black vapor dudes with gold swords. Fine. How do we break those chains?"

Thanatos smiled. "Only the fire of life can melt the chains of death."

"Without the riddles, please?" Percy asked.

Frank drew a shaky breath. "It isn't a riddle."

"Frank, no," Hazel said weakly. "There's got to be another way."

Laughter boomed across the glacier. A rumbling voice said: "My friends. I've waited so long!"

Standing at the gates of the camp was Alcyoneus. He was even larger than the giant Polybotes they'd seen in California. He had metallic golden skin, armor made from platinum links, and an iron staff the size of a totem pole. His rust-red dragon legs pounded against the ice as he entered the camp. Precious stones glinted in his red braided hair.

The giant approached, grinning at them with his solid silver teeth.

"Ah, Hazel Levesque," he said, "you cost me dearly! If not for you, I would have risen decades ago, and this world would already be Gaea's. But no matter!"

He spread his hands, showing off the ranks of ghostly soldiers. "Welcome, Percy Jackson! Welcome, Brooklyn Hayward! Welcome, Frank Zhang! I am Alcyoneus, the bane of Pluto, the new master of Death. And this is your new legion."