Despite his battle scars, the Titan’s face was handsome and strangely familiar. Percy was pretty sure he’d never seen the guy before, but his eyes and his smile reminded Percy of someone.…

The Titan stopped in front of Bob. He clapped him on the shoulder. “Iapetus! Don’t tell me you don’t recognize your own brother!”

“No!” Bob agreed nervously. “I won’t tell you that.”

The other Titan threw back his head and laughed. “I heard you were thrown into the Lethe. Must’ve been terrible! We all knew you would heal eventually. It’s Koios! Koios!”

“Of course,” Bob said. “Koios, Titan of…”

“The North!” Koios said.

“I know!” Bob shouted.

They laughed together and took turns hitting each other in the arm.

Apparently miffed by all the jostling, Small Bob crawled onto Bob’s head and began making a nest in the Titan’s silver hair.

“Poor old Iapetus,” said Koios. “They must have laid you low indeed. Look at you! A broom? A servant’s uniform? A cat in your hair? Truly, Hades must pay for these insults. Who was that demigod who took your memory? Bah! We must rip him to pieces, you and I, eh?”

“Ha-ha.” Bob swallowed. “Yes, indeed. Rip him to pieces.”

Percy’s fingers closed around his pen. He didn’t think much of Bob’s brother, even without the rip-him-to-pieces threat. Compared to Bob’s simple way of speaking, Koios sounded like he was reciting Shakespeare. That alone was enough to make Percy irritated.

He was ready to uncap Riptide if he had to, but so far Koios didn’t seem to notice him. And Bob hadn’t betrayed them yet, though he’d had plenty of opportunities.

“Ah, it’s good to see you.…” Koios drummed his fingers on his bear’s-head helmet. “You remember what fun we had in the old days?”

“Of course!” Bob chirped. “When we, uh…”

“Holding down our father, Ouranos,” Koios said.

“Yes! We loved wrestling with Dad.…”

“We restrained him.”

“That’s what I meant!”

“While Kronos cut him to pieces with his scythe.”

“Yes, ha-ha.” Bob looked mildly ill. “What fun.”

“You grabbed Father’s right foot, as I recall,” Koios said. “And Ouranos kicked you in the face as he struggled. How we used to tease you about that!”

“Silly me,” Bob agreed.

“Sadly, our brother Kronos was dissolved by those impudent demigods.” Koios heaved a sigh. “Bits and pieces of his essence remain, but nothing you could put together again. I suppose some injuries even Tartarus cannot heal.”

“Alas!”

“But the rest of us have another chance to shine, eh?” He leaned forward conspiratorially. “These giants may think they will rule. Let them be our shock troops and destroy the Olympians—all well and good. But once the Earth Mother is awake, she will remember that we are her eldest children. Mark my words. The Titans will yet rule the cosmos.”

“Hmm,” Bob said. “The giants may not like that.”

“Spit on what they like,” Koios said. “They’ve already passed through the Doors of Death, anyway, back to the mortal world. Polybotes was the last one, not half an hour ago, still grumbling about missing his prey. Apparently some demigods he was after got swallowed by Nyx. Never see them again, I wager!”

Annabeth gripped Percy’s wrist. Through the Death Mist, he couldn’t read her expression very well, but he saw the alarm in her eyes.

If the giants had already passed through the Doors, then at least they wouldn’t be hunting through Tartarus for Percy and Annabeth. Unfortunately, that also meant their friends in the mortal world were in even greater danger. All of the earlier fights with the giants had been in vain. Their enemies would be reborn as strong as ever.

“Well!” Koios drew his massive sword. The blade radiated a cold deeper than the Hubbard Glacier. “I must be off. Leto should have regenerated by now. I will convince her to fight.”

“Of course,” Bob murmured. “Leto.”

Koios laughed. “You’ve forgotten my daughter, as well? I suppose it’s been too long since you’ve seen her. The peaceful ones like her always take the longest to re-form. This time, though, I’m sure Leto will fight for vengeance. The way Zeus treated her, after she bore him those fine twins? Outrageous!”

Percy almost grunted out loud.

The twins.

He remembered the name Leto: the mother of Apollo and Artemis. This guy Koios looked vaguely familiar because he had Artemis’s cold eyes and Apollo’s smile. The Titan was their grandfather, Leto’s father. The idea gave Percy a migraine.

“Well! I’ll see you in the mortal world!” Koios chest-bumped Bob, almost knocking the cat off his head. “Oh, and our two other brothers are guarding this side of the Doors, so you’ll see them soon enough!”

“I will?”

“Count on it!” Koios lumbered off, almost knocking over Percy and Annabeth as they scrambled out of his way.

Before the crowd of monsters could fill the empty space, Percy motioned for Bob to lean in.

“You okay, big guy?” Percy whispered.

Bob frowned. “I do not know. In all this”—he gestured around them—“what is the meaning of okay?”

Fair point, Percy thought.

Annabeth peered toward the Doors of Death, though the crowd of monsters blocked them from view. “Did I hear correctly? Two more Titans guarding our exit? That’s not good.”

Percy looked at Bob. The Titan’s distant expression worried him.

“Do you remember Koios?” he asked gently. “All that stuff he was talking about?”

Bob gripped his broom. “When he told it, I remembered. He handed me my past like…like a spear. But I do not know if I should take it. Is it still mine, if I do not want it?”

“No,” Annabeth said firmly. “Bob, you’re different now. You’re better.”

The kitten jumped off Bob’s head. He circled the Titan’s feet, bumping his head against the Titan’s pants cuffs. Bob didn’t seem to notice.

Percy wished he could be as certain as Annabeth. He wished he could tell Bob with absolute confidence that he should forget about his past.

But Percy understood Bob’s confusion. He remembered the day he’d opened his eyes at the Wolf House in California, his memory wiped clean by Hera. If somebody had been waiting for Percy when he first woke up, if they’d convinced Percy that his name was Bob, and he was a friend of the Titans and the giants…would Percy have believed it? Would he have felt betrayed once he found out his true identity?

This is different, he told himself. We’re the good guys.

But were they? Percy had left Bob in Hades’s palace, at the mercy of a new master who hated him. Percy didn’t feel like he had much right to tell Bob what to do now—even if their lives depended on it.

“I think you can choose, Bob,” Percy ventured. “Take the parts of Iapetus’s past that you want to keep. Leave the rest. Your future is what matters.”

“Future…” Bob mused. “That is a mortal concept. I am not meant to change, Percy Friend.” He gazed around him at the horde of monsters. “We are the same…forever.”

“If you were the same,” Percy said, “Annabeth and I would be dead already. Maybe we weren’t meant to be friends, but we are. You’ve been the best friend we could ask for.”

Bob’s silver eyes looked darker than usual. He held out his hand, and Small Bob the kitten jumped into it. The Titan rose to his full height. “Let us go, then, friends. Not much farther.”

Stomping on Tartarus’s heart wasn’t nearly as much fun as it sounded.

The purplish ground was slippery and constantly pulsing. It looked flat from a distance, but up close it was made of folds and ridges that got harder to navigate the farther they walked. Gnarled lumps of red arteries and blue veins gave Percy some footholds when he had to climb, but the going was slow.

And of course, the monsters were everywhere. Packs of hellhounds prowled the plains, baying and snarling and attacking any monster that dropped its guard. Arai wheeled overhead on leathery wings, making ghastly dark silhouettes in the poison clouds.

Percy stumbled. His hand touched a red artery, and a tingling sensation went up his arm. “There’s water in here,” he said. “Actual water.”

Bob grunted. “One of the five rivers. His blood.”

“His blood?” Annabeth stepped away from the nearest clump of veins. “I knew the Underworld rivers all emptied into Tartarus, but—”

“Yes,” Bob agreed. “They all flow through his heart.”

Percy traced his hand across a web of capillaries. Was the water of the Styx flowing beneath his fingers, or maybe the Lethe? If one of those veins popped when he stepped on it… Percy shuddered. He realized he was taking a stroll across the most dangerous circulatory system in the universe.

“We should hurry,” Annabeth said. “If we can’t…”

Her voice trailed off.

Ahead of them, jagged streaks of darkness tore through the air—like lightning, except pure black.

“The Doors,” Bob said. “Must be a large group going through.”

Percy’s mouth tasted like gorgon’s blood. Even if his friends from the Argo II managed to find the other side of the Doors of Death, how could they possibly fight the waves of monsters that were coming through, especially if all the giants were already waiting for them?

“Do all the monsters go through the House of Hades?” he asked. “How big is that place?”

Bob shrugged. “Perhaps they are sent elsewhere when they step through. The House of Hades is in the earth, yes? That is Gaea’s realm. She could send her minions wherever she wishes.”

Percy’s spirits sank. Monsters coming through the Doors of Death to threaten his friends at Epirus—that was bad enough. Now he imagined the ground on the mortal side as one big subway system, depositing giants and other nasties anywhere Gaea wanted them to go—Camp Half-Blood, Camp Jupiter, or in the path of the Argo II before it could even reach Epirus.

“If Gaea has that much power,” Annabeth asked, “couldn’t she control where we end up?”

Percy really hated that question. Sometimes he wished Annabeth weren’t so smart.

Bob scratched his chin. “You are not monsters. It may be different for you.”

Great, Percy thought.

He didn’t relish the idea of Gaea waiting for them on the other side, ready to teleport them into the middle of a mountain; but at least the Doors were a chance to get out of Tartarus. It wasn’t like they had a better option.

Bob helped them over the top of another ridge. Suddenly the Doors of Death were in plain view—a freestanding rectangle of darkness at the top of the next heart-muscle hill, about a quarter mile away, surrounded by a horde of monsters so thick Percy could’ve walked on their heads all the way across.