'Silly me,' Bob agreed.

'Sadly, our brother Kronos was dissolved by those impudent demiG.o.ds.' 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 t.i.tans will yet rule the cosmos.'

'Hmm,' Bob said. 'The giants may not like that.'

'Spit on what they like,' Koios said. 'They've already pa.s.sed 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 demiG.o.ds 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 pa.s.sed 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 ma.s.sive 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 t.i.tan was their grandfather, Leto's father. The idea gave Percy a migraine.

'Well! I'll see you in the mortal world!' Koios chest-b.u.mped 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 s.p.a.ce, 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 towards the Doors of Death, though the crowd of monsters blocked them from view. 'Did I hear correctly? Two more t.i.tans guarding our exit? That's not good.'

Percy looked at Bob. The t.i.tan'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 t.i.tan's feet, b.u.mping his head against the t.i.tan's trouser 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 t.i.tans and the giants ... would Percy have believed it? Would he have felt betrayed once he found out his true ident.i.ty?

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 t.i.tan rose to his full height. 'Let us go, then, friends. Not much further.'

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 further 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 h.e.l.lhounds 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 Gaia'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 Gaia wanted them to go Camp Half-Blood, Camp Jupiter or in the path of the Argo II before it could even reach Epirus.

'If Gaia 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 Gaia 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, surrounding by a horde of monsters so thick Percy could've walked on their heads all the way across.

The Doors were still too far away to make out much detail, but the t.i.tans flanking either side were familiar enough. The one on the left wore shining golden armour that shimmered with heat.

'Hyperion,' Percy muttered. 'That guy just won't stay dead.'

The one on the right wore dark-blue armour, with ram horns curling from the sides of his helmet. Percy had only seen him in dreams before, but it was definitely Krios, the t.i.tan that Jason had killed in the battle for Mount Tam.

'Bob's other brothers,' Annabeth said. The Death Mist shimmered around her, temporarily turning her face into a grinning skull. 'Bob, if you have to fight them, can you?'

Bob hefted his broom, like he was ready for a messy cleaning job. 'We must hurry,' he said, which Percy noticed wasn't really an answer. 'Follow me.'

LXIII.

PERCY.

SO FAR, THEIR DEATH MIST camouflage plan seemed to be working. So, naturally, Percy expected a ma.s.sive last-minute fail.

Fifty feet from the Doors of Death, he and Annabeth froze.

'Oh, G.o.ds,' Annabeth murmured. 'They're the same.'

Percy knew what she meant. Framed in Stygian iron, the magical portal was a set of elevator doors two panels of silver and black etched with art deco designs. Except for the fact that the colours were inverted, they looked exactly like the elevators in the Empire State Building, the entrance to Olympus.

Seeing them, Percy felt so homesick he couldn't breathe. He didn't just miss Mount Olympus. He missed everything he'd left behind: New York City, Camp Half-Blood, his mom and stepdad. His eyes stung. He didn't trust himself to talk.

The Doors of Death seemed like a personal insult, designed to remind him of everything he couldn't have.

As he got over his initial shock, he noticed other details: the frost spreading from the base of the Doors, the purplish glow in the air around them and the chains that held them fast.

Cords of black iron ran down either side of the frame, like rigging lines on a suspension bridge. They were tethered to hooks embedded in the fleshy ground. The two t.i.tans, Krios and Hyperion, stood guard at the anchor points.

As Percy watched, the entire frame shuddered. Black lightning flashed into the sky. The chains shook, and the t.i.tans planted their feet on the hooks to keep them secure. The Doors slid open, revealing the gilded interior of an elevator car.

Percy tensed, ready to charge forward, but Bob planted a hand on his shoulder. 'Wait,' he cautioned.

Hyperion yelled to the surrounding crowd: 'Group A-22! Hurry up, you sluggards!'

A dozen Cyclopes rushed forward, waving little red tickets and shouting excitedly. They shouldn't have been able to fit inside those human-sized doors, but as the Cyclopes got close their bodies distorted and shrank, the Doors of Death sucking them inside.

The t.i.tan Krios jabbed his thumb against the UP b.u.t.ton on the elevator's right side. The Doors slid closed.

The frame shuddered again. Dark lightning faded.

'You must understand how it works,' Bob muttered. He addressed the kitten in his palm, maybe so the other monsters wouldn't wonder who he was talking to. 'Each time the Doors open, they try to teleport to a new location. Thanatos made them this way, so only he could find them. But now they are chained. The Doors cannot relocate.'

'Then we cut the chains,' Annabeth whispered.

Percy looked at the blazing form of Hyperion. The last time he'd fought the t.i.tan, it had taken every ounce of his strength. Even then Percy had almost died. Now there were two t.i.tans, with several thousand monsters for backup.

'Our camouflage,' he said. 'Will it disappear if we do something aggressive, like cutting the chains?'

'I do not know,' Bob told his kitten.

'Mrow,' said Small Bob.

'Bob, you'll have to distract them,' Annabeth said. 'Percy and I will sneak around the two t.i.tans and cut the chains from behind.'

'Yes, fine,' Bob said. 'But that is only one problem. Once you are inside the Doors, someone must stay outside to push the b.u.t.ton and defend it.'

Percy tried to swallow. 'Uh ... defend the b.u.t.ton?'

Bob nodded, scratching his kitten under the chin. 'Someone must keep pressing the UP b.u.t.ton for twelve minutes, or the journey will not finish.'

Percy glanced at the Doors. Sure enough, Krios still had his thumb jammed on the UP b.u.t.ton. Twelve minutes ... Somehow, they would have to get the t.i.tans away from those doors. Then Bob, Percy or Annabeth would have to keep that b.u.t.ton pushed for twelve long minutes, in the middle of an army of monsters in the heart of Tartarus, while the other two rode to the mortal world. It was impossible.

'Why twelve minutes?' Percy asked.

'I do not know,' Bob said. 'Why twelve Olympians or twelve t.i.tans?'

'Fair enough,' Percy said, though he had a bitter taste in his mouth.

'What do you mean the journey won't finish?' Annabeth asked. 'What happens to the pa.s.sengers?'

Bob didn't answer. Judging from his pained expression, Percy decided he didn't want to be in that elevator if the car stalled between Tartarus and the mortal world.