Even the G.o.ds couldn't devise a fate so twisted.

But Gaia wasn't like other G.o.ds. The Earth Mother was older, more vicious, more bloodthirsty. Annabeth could imagine her laughing as they fell into the depths.

Annabeth pressed her lips to Percy's ear. 'I love you.'

She wasn't sure he could hear her but if they were going to die she wanted those to be her last words.

She tried desperately to think of a plan to save them. She was a daughter of Athena. She'd proven herself in the tunnels under Rome, beaten a whole series of challenges with only her wits. But she couldn't think of any way to reverse or even slow their fall.

Neither of them had the power to fly not like Jason, who could control the wind, or Frank, who could turn into a winged animal. If they reached the bottom at terminal velocity ... well, she knew enough science to know it would be terminal.

She was seriously wondering whether they could fashion a parachute out of their shirts that's how desperate she was when something about their surroundings changed. The darkness took on a grey-red tinge. She realized she could see Percy's hair as she hugged him. The whistling in her ears turned into more of a roar. The air became intolerably hot, permeated with a smell like rotten eggs.

Suddenly, the chute they'd been falling through opened into a vast cavern. Maybe half a mile below them, Annabeth could see the bottom. For a moment she was too stunned to think properly. The entire island of Manhattan could have fitted inside this cavern and she couldn't even see its full extent. Red clouds hung in the air like vaporized blood. The landscape at least what she could see of it was rocky black plains, punctuated by jagged mountains and fiery chasms. To Annabeth's left, the ground dropped away in a series of cliffs, like colossal steps leading deeper into the abyss.

The stench of sulphur made it hard to concentrate, but she focused on the ground directly below them and saw a ribbon of glittering black liquid a river.

'Percy!' she yelled in his ear. 'Water!'

She gestured frantically. Percy's face was hard to read in the dim red light. He looked sh.e.l.l-shocked and terrified, but he nodded as if he understood.

Percy could control water a.s.suming that was water below them. He might be able to cushion their fall somehow. Of course Annabeth had heard horrible stories about the rivers of the Underworld. They could take away your memories, or burn your body and soul to ashes. But she decided not to think about that. This was their only chance.

The river hurtled towards them. At the last second, Percy yelled defiantly. The water erupted in a ma.s.sive geyser and swallowed them whole.

VI.

ANNABETH.

THE IMPACT DIDN'T kill her, but the cold nearly did.

Freezing water shocked the air right out of her lungs. Her limbs turned rigid, and she lost her grip on Percy. She began to sink. Strange wailing sounds filled her ears millions of heartbroken voices, as if the river were made of distilled sadness. The voices were worse than the cold. They weighed her down and made her numb.

What's the point of struggling? they told her. You're dead anyway. You'll never leave this place.

She could sink to the bottom and drown, let the river carry her body away. That would be easier. She could just close her eyes ...

Percy gripped her hand and jolted her back to reality. She couldn't see him in the murky water, but suddenly she didn't want to die. Together they kicked upward and broke the surface.

Annabeth gasped, grateful for the air, no matter how sulphurous. The water swirled around them, and she realized Percy was creating a whirlpool to buoy them up.

Though she couldn't make out their surroundings, she knew this was a river. Rivers had sh.o.r.es.

'Land,' she croaked. 'Go sideways.'

Percy looked near dead with exhaustion. Usually water reinvigorated him, but not this water. Controlling it must have taken every bit of his strength. The whirlpool began to dissipate. Annabeth hooked one arm around his waist and struggled across the current. The river worked against her: thousands of weeping voices whispering in her ears, getting inside her brain.

Life is despair, they said. Everything is pointless, and then you die.

'Pointless,' Percy murmured. His teeth chattered from the cold. He stopped swimming and began to sink.

'Percy!' she shrieked. 'The river is messing with your mind. It's the Cocytus the River of Lamentation. It's made of pure misery!'

'Misery,' he agreed.

'Fight it!'

She kicked and struggled, trying to keep both of them afloat. Another cosmic joke for Gaia to laugh at: Annabeth dies trying to keep her boyfriend, the son of Poseidon, from drowning.

Not going to happen, you hag, Annabeth thought.

She hugged Percy tighter and kissed him. 'Tell me about New Rome,' she demanded. 'What were your plans for us?'

'New Rome ... For us ...'

'Yeah, Seaweed Brain. You said we could have a future there! Tell me!'

Annabeth had never wanted to leave Camp Half-Blood. It was the only real home she'd ever known. But days ago, on the Argo II, Percy had told her that he imagined a future for the two of them among the Roman demiG.o.ds. In their city of New Rome, veterans of the legion could settle down safely, go to college, get married, even have kids.

'Architecture,' Percy murmured. The fog started to clear from his eyes. 'Thought you'd like the houses, the parks. There's one street with all these cool fountains.'

Annabeth started making progress against the current. Her limbs felt like bags of wet sand, but Percy was helping her now. She could see the dark line of the sh.o.r.e about a stone's throw away.

'College,' she gasped. 'Could we go there together?'

'Y-yeah,' he agreed, a little more confidently.

'What would you study, Percy?'

'Dunno,' he admitted.

'Marine science,' she suggested. 'Oceanography?'

'Surfing?' he asked.

She laughed, and the sound sent a shock wave through the water. The wailing faded to background noise. Annabeth wondered if anyone had ever laughed in Tartarus before just a pure, simple laugh of pleasure. She doubted it.

She used the last of her strength to reach the riverbank. Her feet dug into the sandy bottom. She and Percy hauled themselves ash.o.r.e, shivering and gasping, and collapsed on the dark sand.

Annabeth wanted to curl up next to Percy and go to sleep. She wanted to shut her eyes, hope all of this was just a bad dream and wake up to find herself back on the Argo II, safe with her friends (well ... as safe as a demiG.o.d can ever be).

But, no. They were really in Tartarus. At their feet, the River Cocytus roared past, a flood of liquid wretchedness. The sulphurous air stung Annabeth's lungs and p.r.i.c.kled her skin. When she looked at her arms, she saw they were already covered with an angry rash. She tried to sit up and gasped in pain.

The beach wasn't sand. They were sitting on a field of jagged black-gla.s.s chips, some of which were now embedded in Annabeth's palms.

So the air was acid. The water was misery. The ground was broken gla.s.s. Everything here was designed to hurt and kill. Annabeth took a rattling breath and wondered if the voices in the Cocytus were right. Maybe fighting for survival was pointless. They would be dead within the hour.

Next to her, Percy coughed. 'This place smells like my ex-stepfather.'

Annabeth managed a weak smile. She'd never met Smelly Gabe, but she'd heard enough stories. She loved Percy for trying to lift her spirits.

If she'd fallen into Tartarus by herself, Annabeth thought, she would have been doomed. After all she'd been through beneath Rome, finding the Athena Parthenos, this was simply too much. She would've curled up and cried until she became another ghost, melting into the Cocytus.

But she wasn't alone. She had Percy. And that meant she couldn't give up.

She forced herself to take stock. Her foot was still wrapped in its makeshift cast of board and bubble wrap, still tangled in cobwebs. But when she moved it, it didn't hurt. The ambrosia she'd eaten in the tunnels under Rome must have finally mended her bones.

Her backpack was gone lost during the fall, or maybe washed away in the river. She hated losing Daedalus's laptop, with all its fantastic programs and data, but she had worse problems. Her Celestial bronze dagger was missing the weapon she'd carried since she was seven years old.

The realization almost broke her, but she couldn't let herself dwell on it. Time to grieve later. What else did they have?

No food, no water ... basically no supplies at all.

Yep. Off to a promising start.

Annabeth glanced at Percy. He looked pretty bad. His dark hair was plastered across his forehead, his T-shirt ripped to shreds. His fingers were sc.r.a.ped raw from holding on to that ledge before they fell. Most worrisome of all, he was shivering and his lips were blue.

'We should keep moving or we'll get hypothermia,' Annabeth said. 'Can you stand?'

He nodded. They both struggled to their feet.

Annabeth put her arm around his waist, though she wasn't sure who was supporting whom. She scanned their surroundings. Above, she saw no sign of the tunnel they'd fallen down. She couldn't even see the cavern roof just blood-coloured clouds floating in the hazy grey air. It was like staring through a thin mix of tomato soup and cement.

The black-gla.s.s beach stretched inland about fifty yards, then dropped off the edge of a cliff. From where she stood, Annabeth couldn't see what was below, but the edge flickered with red light as if illuminated by huge fires.

A distant memory tugged at her something about Tartarus and fire. Before she could think too much about it, Percy inhaled sharply.

'Look.' He pointed downstream.

A hundred feet away, a familiar-looking baby-blue Italian car had crashed headfirst into the sand. It looked just like the Fiat that had smashed into Arachne and sent her plummeting into the pit.

Annabeth hoped she was wrong, but how many Italian sports cars could there be in Tartarus? Part of her didn't want to go anywhere near it, but she had to find out. She gripped Percy's hand, and they stumbled towards the wreckage. One of the car's tyres had come off and was floating in a back-water eddy of the Cocytus. The Fiat's windows had shattered, sending brighter gla.s.s like frosting across the dark beach. Under the crushed hood lay the tattered, glistening remains of a giant silk coc.o.o.n the trap that Annabeth had tricked Arachne into weaving. It was unmistakably empty. Slash marks in the sand made a trail downriver ... as if something heavy, with multiple legs, had scuttled into the darkness.

'She's alive.' Annabeth was so horrified, so outraged by the unfairness of it all, she had to suppress the urge to throw up.

'It's Tartarus,' Percy said. 'Monster home court. Down here, maybe they can't be killed.'

He gave Annabeth an embarra.s.sed look, as if realizing he wasn't helping team morale. 'Or maybe she's badly wounded, and she crawled away to die.'

'Let's go with that,' Annabeth agreed.

Percy was still shivering. Annabeth wasn't feeling any warmer either, despite the hot, sticky air. The gla.s.s cuts on her hands were still bleeding, which was unusual for her. Normally, she healed fast. Her breathing got more and more laboured.

'This place is killing us,' she said. 'I mean, it's literally going to kill us, unless ...'

Tartarus. Fire. That distant memory came into focus. She gazed inland towards the cliff, illuminated by flames from below.

It was an absolutely crazy idea. But it might be their only chance.

'Unless what?' Percy prompted. 'You've got a brilliant plan, haven't you?'

'It's a plan,' Annabeth murmured. 'I don't know about brilliant. We need to find the River of Fire.'

VII.

ANNABETH.

WHEN THEY REACHED THE LEDGE, Annabeth was sure she'd signed their death warrants.

The cliff dropped more than eighty feet. At the bottom stretched a nightmarish version of the Grand Canyon: a river of fire cutting a path through a jagged obsidian creva.s.se, the glowing red current casting horrible shadows across the cliff faces.

Even from the top of the canyon, the heat was intense. The chill of the River Cocytus hadn't left Annabeth's bones, but now her face felt raw and sunburnt. Every breath took more effort, as if her chest were filled with styrofoam peanuts. The cuts on her hands bled more rather than less. Annabeth's ankle, which had almost healed, now seemed to be broken again. She'd taken off her makeshift cast, but now she regretted it. Each step made her wince.

a.s.suming they could make it down to the fiery river, which she doubted, her plan seemed certifiably insane.

'Uh ...' Percy examined the cliff. He pointed to a tiny fissure running diagonally from the edge to the bottom. 'We can try that ledge there. Might be able to climb down.'

He didn't say they'd be crazy to try. He managed to sound hopeful. Annabeth was grateful for that, but she also worried that she was leading him to his doom.

Of course if they stayed here they would die anyway. Blisters had started to form on their arms from exposure to the Tartarus air. The whole environment was about as healthy as a nuclear blast zone.

Percy went first. The ledge was barely wide enough to allow a toehold. Their hands clawed for any crack in the gla.s.sy rock. Every time Annabeth put pressure on her bad foot, she wanted to yelp. She'd ripped off the sleeves of her T-shirt and used the cloth to wrap her b.l.o.o.d.y palms, but her fingers were still slippery and weak.

A few steps below her, Percy grunted as he reached for another handhold. 'So ... what is this fire river called?'

'The Phlegethon,' she said. 'You should concentrate on going down.'

'The Phlegethon?' He shinned along the ledge. They'd made it roughly a third of the way down the cliff still high enough up to die if they fell. 'Sounds like a marathon for hawking spitb.a.l.l.s.'

'Please don't make me laugh,' she said.

'Just trying to keep things light.'

'Thanks,' she grunted, nearly missing the ledge with her bad foot. 'I'll have a smile on my face as I plummet to my death.'

They kept going, one step at a time. Annabeth's eyes stung with sweat. Her arms trembled. But, to her amazement, they finally made it to the bottom of the cliff.