Nico had walked for a few hours over the grim and lifeless terrain, past his father’s palace and the Fields of Asphodel, before he’d found the cave.‌

He wasn’t sure what he’d been expecting. The entrance to Tartarus looked like … well, a hole in the ground. Nothing special. Surrounded by enormous boulders, the pitch-black entrance sank into the earth at a steep

angle. Maybe the air coming out of it was a little warmer than the rest of the Underworld, like the exhalations of a living creature. Otherwise … yeah. It was a cave. Very cave-like, all things considered.

So this was it. For the entrance to the worst place in all existence, it felt oddly anticlimactic. But if the Doors of Death were down there, then maybe Nico could close them and stop Gaia before things got worse.

Things always get worse, he thought. Don’t let your guard down.

The irony, of course, was that as he stood there, worried about what lay ahead of him, he didn’t sense the thing coming up behind him.

By the time he heard its hiss and spun around to meet it, the Chimera was upon him.

It was twice Nico’s size, its lion’s maw caked in dirt and blood. Its

shaggy goat body swarmed with blow flies, and its scaly tail lashed back and forth like a diamondback rattlesnake.

Nico whipped out his Stygian iron sword, but it didn’t matter.

It was the tail of the other monster that caught him across the chest.

Nico slammed against the nearest boulder, the breath knocked out of him. ‘Nico di Angelo,’ said a gloating voice. ‘This time, you don’t have

anywhere to escape to!’

He tried to suck in air, but it was like a giant had clasped their hands

around his chest. He pushed himself upright, pointing the tip of his sword towards …

Nonna?

Nico immediately felt ashamed for making that comparison, but the

creature looming over him did look a lot like his grandmother back in 1930s Venice. Her coiffed hair was gunmetal grey, her stout upper body clothed in a faded flower-print dress and a hand-knitted sweater. But Nico’s grandmother hadn’t had eyes slitted like a reptile’s, a flickering forked tongue, or a massive snake’s trunk instead of legs.

‘You know,’ said Nico, ‘you could just say hello instead of trying to kill me.’

‘I am the Mother of Monsters,’ she said, her voice thick with bile. ‘You will address me as Echidna!’

‘Like that hedgehog animal?’

She cast a baleful glare at her Chimera companion. ‘Every time! Why do they say that every time?’

‘Well,’ Nico said, ‘you did name yourself after the animal.’

This seemed like a reasonable point to Nico, but, judging from the way Echidna bared her fangs, she did not agree.

‘First of all, it’s not a hedgehog,’ she said. ‘It’s related to the anteater.

Secondly, Australia named it after me. Do you honestly think I would allow myself to be linked to such a lowly creature?’

‘Hedgehogs are pretty cute,’ he said, his mind running calculations on how he could get out of this mess without being slaughtered. ‘I’d be flattered.’

‘This is why I hate demigods,’ she said. ‘You think you can joke and distract your way out of everything. That Percy Jackson also thought he could escape me.’

At the mention of Percy’s name, Nico’s heart skipped a beat. ‘From what I heard … he didn’t “escape”, because you never actually captured him.’

She sneered. ‘A mere technicality.’

‘I don’t know. If you look up the definition of the word escape –’ ‘Enough!’ Echidna roared. ‘If I wanted you dead, Nico di Angelo, I

would have already killed you. We are only here to bear witness, and to make sure you don’t lose your nerve.’

The Chimera stepped forward, forcing Nico back towards the cave’s entrance. The warm breeze from the chasm seemed to wrap around him, pulling him closer.

‘Do you sense it now?’ asked Echidna, her forked tongue darting between her fangs. ‘That is your destiny …’

Nico’s feet slid against the dirt as if he were already on an incline. He tried to take a step forward, but it was pointless. His feet slipped out from under him and he nearly cracked his jaw on the ground.

Echidna laughed. ‘You’re right where Gaia wants you!’

Nico dug his fingers into the dirt, but he was moving too quickly. ‘Say hello to all my monster friends!’ she called.

The terrible gravity of Tartarus grasped Nico, and he plunged into the pit.

He fell.

Not for long.

For an eternity.

At last, he crash-landed against a hard surface, and for the second time that day he got the wind knocked out of him. Every bone in his body should have been broken, but somehow he forced himself to move.

He got to his hands and knees. His muscles screamed in protest.

Something slithered past him in the darkness, grazing his shoulder. He

swung his sword in that direction, hoping to strike something. A piercing shriek was his answer.

He hoisted himself up, scrambling for purchase on the rough ground. In the purple glow of his blade, all he could see were shadows dancing around him.

‘Who’s there?’ Nico yelled.

He was met with laughter – a sick, phlegmy sound. As he moved forward, his sword held aloft, something brushed his neck. He screamed and swatted at it. Then a voice giggled in his other ear. It sounded like a demonic toddler.

Knowing his luck, it probably was.

Nico pressed on until he perceived a dim light in the distance. Still, he could see nothing of his surroundings. He’d thought he understood darkness, but now he realized he’d been thinking of the shadows here all

wrong. They didn’t recede in the glow of his blade. Instead, they thickened stubbornly, clinging to him like some sort of mist or fog.

It was as if Tartarus were alive, sending antibodies to attack him as a foreign invader. He trudged forward towards the distant red glow. The scent on the breeze turned sharp and bitter.

Finally, he staggered out of the shadow fog. Nico nearly collapsed at what he saw.

Spreading to the horizon was a blood-red landscape of hills and crags, dotted with twisted, blackened trees. Noxious green clouds drifted through the air and clung to the valleys. And just below him, on a flattened plain of crushed rock and volcanic glass, Gaia’s army was preparing for war.

Hyperborean giants towered above the other troops like living blue siege towers. Legions of Cyclopes rummaged through mounds of armour and

weapons, looking for the best-quality gear. Packs of wolves prowled the perimeter, occasionally surrounding some unfortunate monster straggler and taking them out for lunch. A herd of drakons wove in and out of the ranks, trampling anything too slow to get out of their way.

‘Oh, Hades,’ Nico murmured.

Which was exactly when three basilisks raised their heads to look at him. Nico knew what they were instantly – not many creatures look like cobras with miniature deer antlers – but he knew better than to meet their yellow lamp-like gaze.

Instead, he turned and ran.

He heard their blood-chilling screeches behind him, but he refused to look back. Whatever he was running towards, it had to be better than the ten-thousand-to-one odds behind him.

The ground gave with each step like spongy turf. Off to his left, a green bank of fog drifted across a marsh. He thought of heading into it, for cover at least, but he didn’t know what that fog was made of. It could be acid, or poison, or some monstrous gaseous life-form with a taste for demigods.

Behind him, a beast snarled. Nico instinctively swung his sword back, and the blade connected with flesh. The creature howled in pain. Another

lunged in front of him: one of the massive black wolves. Nico sliced off its head without even slowing, and its body disintegrated immediately.

Nico kept running. Sweat poured down his face. His lungs burned. He glanced back just long enough to see more wolves racing after him,

slavering for a di Angelo snack plate.

Absolutely not, he told himself.

But there was nowhere to go, nothing to hide behind. About a hundred metres away, he spotted a ridge with some strange black ovals protruding from the surface. Volcanic outcrops, maybe? Perhaps something there could give him a bit of coverage, but he’d never make it before the wolves tore him apart.

Then he glanced to his right and nearly tripped over himself in surprise.

Someone was waving at him.

Nestled between the nearest two hills was a white house with red trim, big bay windows and a sloping, shingled roof. Unlike everything else in Tartarus, it didn’t appear dead, rotting or poisonous. It was just … a house,

like you might see anywhere in suburban America. On the front porch stood a human-looking figure, beckoning to Nico. He knew in his heart this was probably a trap, but where else was he supposed to go?

His lungs burned.

His eyes watered.

He was losing hope as the wolves gained ground.

So Nico cut to the right and pumped his legs. He could hear the wolves’ paws thumping behind him. He pushed himself harder, until the person on the porch was fully in view. They had shoulder-length black hair and a

striking red jacket that matched the surrounding landscape. As Nico got

closer, they turned and walked through the front door, which began to close

…

‘Hey!’ Nico yelled. ‘Wait!’

He was running so fast he almost flew through the doorway. It slammed shut, just in time for the wolves to crash into it.

They howled and whined outside while Nico sat panting on the floor, his back wedged against the door. Why did his lungs hurt so badly? Maybe he’d cracked his ribs in the fall. Or maybe the atmosphere in Tartarus just

wasn’t fit for demigods. Maybe he was supposed to struggle to survive here.

He glanced around at the empty room: nothing but a bare, dusty hardwood floor and blank white walls. No other exits. Even the bay windows seemed to have disappeared from the front wall.

‘About time you found me.’

The voice startled Nico so badly that he jumped and banged his head on the doorknob. Clutching the tender spot on the top of his skull, he squinted at the person who had materialized across the room.

She didn’t look like a monster, which concerned Nico, given that he’d fallen into Tartarus. Then again, monsters came in all shapes and sizes. Her jeans and leather boots were the same dark tone as her hair. A single gold

chain looped across the front of her white blouse. Her red jacket glistened disturbingly like fresh blood. Behind her was … nothing. The back wall had simply vanished, replaced by a dark void.

She stared at Nico appraisingly. ‘Well? Aren’t you going to ask me who I am?’

Nico rubbed the knot forming on his head. ‘I’m going to guess you’re a goddess, seeing as you have a house in the middle of Tartarus. Is this, like, your vacation home or …?’

‘It’s not really my home,’ she said. ‘Think of it more as … a shrine, if you will. A safe haven. And until recent events I was not allowed even that.’

As she said this, her irises flared red. ‘My only true home is in the heart, the spirit. When balance is achieved.’

The flare went out.

‘Impressive,’ said Nico. When she rolled her eyes, he laughed. ‘I’m serious! That was actually pretty cool.’

‘Leave it to Nico di Angelo to tell a goddess that they’re “cool”.’

He examined her sharp, angular face. The dark eyes. The dark hair. The obsession with balance.

‘You’re Ethan Nakamura’s mother,’ he decided. ‘Nemesis.’

She opened her arms wide. ‘In the flesh. Or not, depending on how you view godhood.’

Nico got to his feet. He wasn’t usually one to feel starstruck – or godstruck – but an unfamiliar sensation was creeping through him: awe.

‘Why are you here?’ he asked. ‘Why did you save me?’ ‘Can’t a goddess do something nice for a demigod?’

Nico barked a laugh. ‘Yeah, but it always comes with a catch. I’m not a fool, Nemesis.’

She stepped towards him, and the field of darkness came with her, drifting behind her body like the train of a dress. The house changed. No longer was Nico in an empty room. He stood on the parapets of Erebos, the

walls of impenetrable darkness marching off in either direction. He gazed across the Fields of Asphodel, towards the spires of his father’s palace.

‘Why have you brought me here?’ he murmured.

But when he turned for the answer, Nemesis was gone. Instead, his father stood before him.

Hades’s robes swirled with ghostly afterimages of the damned. His dark beard was longer, which startled Nico, since he had seen his father only a day or so ago. But of course gods could look like whatever they wanted,

and this god wasn’t his father at all.

‘What is this, Nemesis?’ Nico demanded. ‘Why do you look like that?’

The false Hades spoke with Nemesis’s voice. ‘I know what you really want,’ she said. ‘I know the imbalance that exists in your heart.’

As if to prove her point, Nico’s heartbeat stumbled. He wondered how deeply Nemesis could see into his feelings, and why she’d chosen to stand in judgement in the guise of his father.

‘I don’t know what you mean,’ he said.

Nemesis/Hades chuckled. ‘I have taken a greater interest in demigods since Percy Jackson advocated on behalf of us so-called minor gods to those snobs on Mount Olympus. I have come to believe that you heroes may be more … interesting than I thought. And you in particular wish to right what was made wrong.’

Nico’s mouth tasted of ashes. ‘But why show me this? Why my father?’

Nemesis swept her hand across the landscape of Erebos. ‘To demonstrate what you already know. Your father tries, but even here, in the place of final judgement, true fairness is so rarely achieved. The good suffer. The bad are rewarded. The gods’ great system is a creaky machine, a lopsided wheel. At times, we must act individually – you must act – to achieve a proper justice. Just as you are doing now.’

‘Enough,’ Nico said, heat flushing his cheeks. ‘If you want to help me, get me to the Doors of Death.’

Nemesis’s smile faded. Darkness swept around them, and suddenly she was back in her original form, staring at Nico across the bare room of her suburban Tartarus sanctuary.

‘There are limits to how much I can help you,’ she said, ‘especially in Tartarus.’

She moved closer to Nico, her stare burning into him. ‘I am the goddess of retribution,’ she said. ‘This is the realm in which monsters regenerate

after they’ve been disposed of by gods or demigods. All of them desire

nothing but retribution, Nico.’

‘So wouldn’t that make you more powerful here?’

She frowned. ‘It’s the opposite. Each moment I spend here, I am torn in every direction. I can feel my body ripping apart right now.’

‘I can relate,’ Nico grumbled. His lungs hurt with every breath. He found himself leaning on his sword just to stay up.

There was a brief flash of pity in the goddess’s eyes. ‘You have a terrible journey ahead of you and, in the short term, I sense it will cause even more injustice and misery.’

‘Great,’ groaned Nico.

‘But listen to me, demigod.’ Her voice turned sharp and chiding. ‘You must endure.’ She grabbed Nico’s hand, and he was shocked by how warm it was. She pressed something into his palm. ‘Keep these with you all the time. You will need them.’

He looked at what she had given him: three glistening red seeds –

pomegranate seeds.

‘From your stepmother’s garden,’ Nemesis explained.

‘I know what they are.’ Nico could feel their power radiating along the lines of his palm.

He knew that, as a child of Hades, he could use each one to put himself into a daylong death trance, a sort of hibernation, if necessary. But … why? Why was she giving him these?

There was a loud THUD behind him. The front door shuddered on its hinges. Outside, he could hear the wolves snarling, preparing for another assault.

‘We are almost out of time,’ Nemesis said. ‘Follow the River of Fire,

Nico. Follow it downstream, through the mist and the forest. There you will find the Doors of Death.’

Nico jumped as the door began to splinter. Through one of the cracks flashed the baleful yellow eye of a wolf.

‘I will get you away from here, Nico,’ said Nemesis. ‘But one day you will need to deal with the imbalance in your heart.’

Nico closed his fingers around the pomegranate seeds, then tucked them away with the others he kept. There was much more he wanted to ask, but he also wanted to be far, far away from this place as soon as possible.

‘Thank you,’ he said. ‘I appreciate the help.’

Nemesis raised her hands, and the darkness began to swirl around them. ‘One last thing … Beware of my mother. She only comes out during the daytime and … let’s just say she is not as sympathetic to demigods as some of her children are.’

‘Daytime?’ Nico asked. The concept made no sense to him down here, in the darkest depths of Underworld.

But the house disappeared, and Nemesis with it. Nico found himself

standing on a ridge, the spongy red ground once again under his feet. There were no wolves or other monsters in sight, but spread across the hills in

every direction were the strange black oval outcrops he’d seen from a distance. He edged closer to the nearest one and peered down at its surface

…

‘Ugh, gross,’ he said.

It was as if the land itself had a pimple. The substance wasn’t rock,

exactly – more like a dark translucent membrane covering an area the size of a bathtub. And, underneath, some sort of sickening yellow-green fluid was pulsing around a shadowy figure suspended within.

‘What the –?’ Nico made a terrible mistake, but he couldn’t resist. With the tip of his sword, he poked the Tartarus zit.

Predictably, the membrane burst, unleashing a geyser of goo that splattered him from head to toe.

‘You’ve got to be kidding me!’ Nico stumbled backwards, landing hard on his tailbone. He watched in horror as something very much alive crawled out of the goo pit.

It shook its sticky wet hair, which began to smoulder and then caught fire. Its form was human, but with mismatched back legs: one shaggy and hooved like a donkey’s, the other constructed of bronze.

An empousa.

Nico’s grip tightened on his sword. He’d been kidnapped by one of these vampiric spirits after foolishly following Minos into the Labyrinth, and he was in no mood to be charmspoken to death.

Taking advantage of the creature’s disorientation, he scrambled forward and drove his blade through its chest.

The creature wailed. ‘I just regenerated!’ she screamed. ‘Come on!’ Then she crumbled into clumps of dust that broke apart in the goo.

Immediately, the fluid began to ooze back into the pit, and the membrane began weaving itself together.

Wonderful, said Nico to himself. Monsters regenerate even faster in Tartarus.

He scanned his surroundings with a mounting sense of dread.

The landscape was covered with these regeneration zit pits. He had to keep moving.

The only thing that gave him a little bit of hope was the sight of a glowing red ribbon of flames in the distance, threading across the plains. At least Nemesis had deposited Nico within sight of the river he was supposed to follow: the fiery Phlegethon.

Nico pulled his leather jacket tighter and started walking.