Disclaimer: I don't own Percy Jackson. Some of the dialogue in this chapter is taken directly from The Mark of Athena; I don't own that either.

A/N: So I don't really know where this came from, but... I love Nico? This is going to be a multi-chapter story covering his time aboard the Argo II during HoH. I hope you enjoy, and please do leave a review!

Chapter I

Air – he had air again. Aches riddled his exhausted body, and he could not summon the strength to open his eyes, but his lungs had realised that there was fresh air all around him. He took his first deep breath in a week.

All Nico wanted was to lie there on the hard floor beneath him, letting the pain in his hollow chest dissipate, but the back of his neck prickled. He was still in danger.

He struggled onto his hands and knees – even that small movement took a Herculean effort – and began, very slowly, to crawl. He thought he could hear a hissing sound behind him, and a vague image swam to the forefront of his bleary consciousness: his captors, the twin giants Otis and Ephialtes. They had snakes for feet. Snakes hissed, didn't they?

Then the hissing was replaced by predatory growls, and he tried, desperately, blindly, to quicken his pace. The room around him – yes, the bronze jar in which they'd held him had been in a vast underground room – exploded with noise. Yelling and snarling and the clash of metal on metal. Thundering – thunder, underground? There were hands around his shoulders, dragging him to a side, and sharp fear rose in his throat; but these fingers were smaller and warmer than the giants', and anyway he had no strength to resist.

Suddenly there was a gasp close beside him and the grip on his shoulders loosened. The thundering sound got louder – no, not thunder, it was the sound of heavy objects falling around him. That didn't make him feel any safer.

He opened his eyes. He was lying slumped on one side, surrounded by sandbags. This was the giants' room, then – the hypogeum, that was what they'd called it. Not far away, a girl with choppy brown hair was also lying on one side. Her shoulder was bent at an odd angle. The blond boy leaning over her – was that Jason Grace, the missing Roman praetor? – touched her shoulder and she let out a high-pitched yelp, but then said, "Fine. I'm fine."

Nico sat up. The hypogeum was a wreck. Piles of rubble lay scattered at random intervals, and there was no sign of the twins. And there – Nico's heart gave a sudden painful twist. Percy Jackson was standing at the far side of the room, looking warily around. His black hair was tousled and his eyes were as sea-green as ever, and he was as tense and primed for battle as he'd been the first time Nico met him, in the snows outside Westover Hall.

Simultaneously, a mound of dust took shape as the giant Ephialtes, and Otis burst out from under a pile of rubble. Nico fumbled for his sword – where was it? Had they taken it from him once he'd fallen into unconsciousness? Anyway, he doubted he'd be able to stand, let alone raise it.

"Percy!" shouted Jason Grace. "The controls!"

Percy blinked and then drew his bronze sword, Riptide. He slashed it across the control board he was standing behind.

"No!" wailed Ephialtes. "You've ruined the spectacle!"

He swung his spear at Percy and the son of Poseidon fell to his knees, his face suddenly drawn with pain. Jason left the side of the brown-haired girl and ran over to him.

Nico felt suddenly, perilously close to a panic attack. When he'd been captured, he'd been th only demigod alive to know of the existence of both camps, and now Jason Grace and Percy Jackson were fighting side by side. And how had they reached Rome? What were they doing here? His brain felt sluggish and slow, but his heart was thumping far too fast.

"You're both dead," Percy was saying, his voice low and fierce. "I don't care if we have a god in our side or not."

"Well, that's a shame." A god was descending on a platform from the ceiling – Nico didn't recognise him, but there was no mistaking the divine fire flickering in his eyes. "I'd hate to think I made a special trip for nothing."

Two leopards – leopards? Where had they come from? – padded over to him and he scratched their ears. "Really, Ephialtes. Killing demigods is one thing. But using leopards for your spectacle? That's over the line."

The giant choked. "This is impossible. D-D—"

"It's Bacchus, actually, my old friend," said the god. Bacchus... the Roman version of Dionysus. Not the most likely divine champion.

Nico momentarily blacked out. When his vision cleared again, Percy was saying angrily, "What do you consider impressive?"

"Ah, a good question..." said the god. "Perhaps you need inspiration! The stage hasn't been properly set. You call this a spectacle, Ephialtes? Let me show you how it's done."

Nico blinked, and when he opened his eyes again he was no longer in the hypogeum; instead, he was sitting on the stone seats in the old Colosseum, the summer sun beating down on his head. Bacchus was reclining in an elaborate gilded throne to his right, and to Nico's left was the girl with the brown hair, a nymph in a nurse's uniform bandaging her shoulder.

The floor of the hypogeum ascended to show Percy and Jason standing side by side with their swords drawn, facing Otis and Ephialtes. They stared up at Bacchus. The rest of the Colosseum was filled with purple Roman Lares, who fell silent as Bacchus raised a can of Diet Pepsi.

Percy's glare could have stopped rivers – not that he needed help doing that. "You're just going to sit there?" he demanded.

"The demigod is right!" Ephialtes shouted. "Fight us yourself, coward! Um, without the demigods."

"Juno says she's assembled a worthy crew of demigods," Bacchus responded lazily. "Show me. Entertain me, heroes of Olympus. Give me a reason to do more. Being a god has its privileges."

The ghostly crowd cheered.

For a moment, all four combatants stood stock-still, glaring at each other. Nico took the opportunity to turn to the girl on his right and say, "I'm sorry, w-what—"

His voice was weaker than he expected, thin and raspy with disuse. Somehow, she still heard it. She turned to face him, and Nico blinked. He didn't usually notice what girls looked like, but anyone could tell that this girl was seriously pretty: she had long dark hair braided with a white feather, rosy skin and eyes that seemed to shift in colour, blue and green and grey. She smiled at him. "Easy," she said. Her voice was rich and melodious and very soothing. "You're Nico di Angelo? My name is Piper. We're here to save you. We're on your side."

Nico felt his muscles loosen. He leaned back against the stone bench, the panicked feeling in his throat subsiding.

Then Piper gasped and tensed beside him. The twins had just hurled a huge plastic mountain at Percy and Jason.

The two boys dived into a trench. Nico took the opportunity to study Piper more thoroughly. She was biting her lip, looking quite pale with fear, and Nico remembered how Jason Grace had leaned over her in the hypogeum. Her boyfriend? But he was sure he'd never seen her at the Roman camp... In one hand she gripped a strange brown object, almost like a hollowed-out horn. Nico wondered if it was some sort of instrument, but she clutched it like a weapon. A bronze dagger hung at her belt. Not very Roman at all.

Percy and Jason charged out of the trench. The giants had picked up another plastic mountain, but before they could throw it Percy caused a water pipe to burst at their feet, and Otis stumbled backwards, dropping the mountain on his brother. The crowd of ghosts roared.

Otis roared and threw his spear at the boys, but they backed away towards a small lake in the arena floor, shouting insults. Nico caught the words "Swan Lake" and wondered if he was hallucinating.

Jason Grace, who Nico remembered was a son of Jupiter, summoned a blast of wind that shoved Otis into the lake. Percy and Jason brought their blades down together on his head and he crumbled into dust. Nico knew it wouldn't last, though. The demigods needed Bacchus' help to permanently kill the giants.

His heart was beating painfully as he watched Percy charge Ephialtes; his spear clashed with the boys' swords in a brief flurry of action before Jason suddenly stumbled back, blood running down his chest. Beside Nico, the girl Piper screamed.

Ephialtes loomed over the two demigods. Percy was facing Nico, and he looked pale with despair. It was not a look Nico liked to see on his face.

He must be hallucinating. There was no way a Greek trireme could really be descending from the sky above the Colosseum. Still, its shadow felt real enough. What was that as its figurehead – the head of a bronze dragon? The name Argo II was painted on its hull.

Then it fired its ballistae.

Percy and Jason dived for cover, but Ephialtes caught the full blast of the shot. He fell with a thud, groaning. Nico was feeling dizzy. As the warship landed on the arena floor, four figures became visible on deck – and one of them was his sister, Hazel. Her smile stretched from ear to ear.

It was too much, too much. He did not know what he was doing here, and he certainly didn't know why Hazel was here when he'd left her about to embark on a quest from New Rome. Percy had been on that quest, hadn't he?

Nico's fingers were starting to feel cold. Now Bacchus was parading jubilantly around the stadium, saying, "Of course I did something. I killed two giants!"

The ghosts cheered.

"Come on," said Piper. With a jolt, Nico realised she was talking to him. In a daze, he followed her down the stone steps onto the arena floor.

Jason ran to meet them. Although the guy had just been through a battle, his bright blue eyes sparked with energy. "Pipes – you okay?"

"I'm fine," Piper said impatiently. "But your wound—"

"I'll be okay," said Jason. "It's not deep." He glanced at Nico and smiled awkwardly. Nico was used to that.

Nico didn't have the energy to speak, to do anything more than fight to stay upright. Black spots were dancing in his vision, but he stared at the other cluster of demigods. Bacchus had disappeared, as had his ghostly audience. Percy was talking to a short Latino boy with a shock of black hair and a completely manic grin. Hazel and Frank Zhang were standing beside him.

"Where's Annabeth?" Percy demanded, his voice carrying over the distance between them.

Nico's heart felt suddenly cold. Annabeth Chase. Even after his seven months' disappearance, Percy still cared. Of course he did.

The floor was shaking now. "Let's get on board," Piper said urgently. She and Jason ran for the rope ladder extending down the side of the ship, and Nico hobbled after them.

As he reached the ladder, a warm hand touched his wrist. Nico hated physical contact, but he didn't mind when he turned to see Hazel's warm golden eyes smiling into his. "Nico," she said. Just his name, like a prayer.

He couldn't speak; his throat was suddenly tight. He twined his fingers through hers.

"Come on," Hazel said. "Let's get you to safety."

He had to be practically hauled up the ladder. Leaning on Hazel, he hobbled over to the stern of the ship, where she sat him down on a low bench and pulled some ambrosia from her backpack.

Nico had brought food with him from Los Angeles when he'd gone into the Underworld, but after he'd been drawn into that place, the place he had to keep in a locked-up corner of his mind or he would go insane, he hadn't eaten. He didn't think he'd wandered long down there before his capture, and since then, he'd only had the magic pomegranate seeds in the giants' bronze jar.

Logically, he knew he was more than half-starved. But staring at the chunks of ambrosia he realised that he didn't feel hungry.

"Here," Hazel murmured. She pressed a piece to his mouth and he swallowed obediently. It tasted, like it always did, of spaghetti bolognese, both his and Bianca's favourite dish. Bittersweet, like it always was. But he could not think of Bianca now or he would fall into a million pieces and they would never be able to sweep up the fragments.

"Hazel... what is this ship?" he asked. He didn't realise how quiet his voice was until Hazel leaned in to catch his words. Her lovely eyes were dark with worry, worry for him. The thought warmed him a little, though his fingers still felt numb and his head was heavy.

"Do you know the Prophecy of Seven?" she asked. Nico nodded. He'd been there when Rachel Dare had first recited it, and later he'd learned that the Romans had known it for hundreds of years. Hazel wetted her lips. "We – me, Percy, Frank, Jason, Piper, Leo and Annabeth Chase are the seven of the prophecy. Leo – he's a Greek demigod, not Roman like us, and so are Percy and Piper and Annabeth – he built this ship so we could fly to the ancient lands and hopefully defeat the giants."

"Hazel," Nico said gently, "you know that I'm a Greek demigod too, don't you? I'm the son of Hades, not Pluto. I've known Percy and Annabeth for years." He thought he managed to say all this without his voice giving him away.

Hazel's eyes darkened again. "I know," she murmured, and Nico wondered if she was angry with him. The thought was almost more than he could bear.

"I'm sorry," he whispered.

To his relief, his sister smiled at him. "It's alright. You did what you had to do. But where have you been, Nico? You said you'd search for the Doors of Death from the other side, and then Gaia told me in a vision that you'd been captured... did you find them? Where are they?"

Nico stared over her head. The ship was flying high above the city of Rome. Everything seemed so peaceful, the bright blue sky and the Italian sun.

"Nico?"

He met her eyes again. "The darkest part of the Underworld," he said, voice very low. "Where even Hades doesn't venture. They're... they're in Tartarus."

Hazel gasped. "You've been there? To Tartarus? Gods, Nico..."

He didn't want to talk about it. He didn't want to remember, and they were pressing against the edges of his consciousness now, the memories of what he'd seen there. He couldn't let them in.

He forced himself to continue. "The Doors have two sides," he told his sister. "One... one there, and one in the mortal world, in Greece. Gaia has huge forces guarding both sides... they overwhelmed me as soon as I got near. Then they brought me through into the mortal world and took me to Rome, and the giants stuck me in that jar." His hands were trembling now. Hazel pressed them between hers, warm and steady.

"He reads Chinese," the boy called Leo was telling the other demigods. Did he ever stop grinning?

Frank Zhang hunched his shoulders. "Just a little bit."

"How cool is that?" Leo exclaimed.

"Guys," Hazel called. "I hate to interrupt your admiration session, but you should hear this."

She put a hand beneath Nico's elbow, helping him to his feet. He had to lean on her to shuffle the few steps over to the other demigods... and to Percy.

Nico didn't like being stared at, and he didn't like being the centre of attention. His rescuers were looking him with pity and curiosity mingled in their gazes. He took a breath. Never, he thought, would he take a wide expanse of air for granted again.

"Thank you," he said, looking around the group. "I'd given up hope."

Percy was looking intently at him. Nico tried to meet his gaze levelly. He tried not to blush.

"You knew about the two camps all along," Percy said. To his credit, there was no hint of accusation in his voice, just a sort of detached curiosity. "You could have told me who I was the first day I arrived at Camp Jupiter, but you didn't."

Hazel wasn't holding Nico's elbow any more. He swayed and then slumped against the ship's helm. "Percy, I'm sorry. I discovered Camp Jupiter last year. My dad led me there, though I wasn't sure why. He said the gods had kept the camps separate for centuries and that I couldn't tell anyone. The time wasn't right. But he said it would be important for me to know..." He'd been talking too much; his lungs couldn't stand the strain. A spasm of coughing broke out, and he doubled over, but Hazel was there, holding him until it passed. "I – I thought Dad meant because of Hazel," he carried on. "I'd need a safe space to take her. But now... I think he wanted me to know about both camps so I'd understand how important your quest was, and so I'd search for the Doors of Death."

Sparks flew from Jason Grace's hands. Nico wondered if that often happened when he was nervous, and if it was safe for him to stand near plug sockets.

"Did you find the doors?" asked Percy.

Nico nodded. "I was a fool," he said bitterly. "I thought I could go anywhere in the Underworld, bit I walked right into Gaia's trap. I might as well have tried running from a black hole."

Frank chewed his lip. "Um... what kind of black hole are we talking about?"

Nico wanted to answer him, but the words stuck in his throat. The memories were hissing at him louder now, begging his fragile consciousness to give in to their onslaught. He fought back a shudder and turned to his sister.

Hazel put a hand on his arm and began to explain to the others about the mortal side of the doors.

Piper's horn spat out a cheeseburger. Not a musical instrument, then. "Where exactly in Greece is this doorway?" she asked.

Nico took a breath. "The House of Hades. It's an underground temple in Epirus. I can mark it on a map, but – but the mortal side of the portal isn't the problem. In the Underworld, the Doors of Death are in... in..." He couldn't say it, he couldn't.

Percy's eyes turned dark. "Tartarus," he murmured. "The deepest part of the Underworld."

Nico nodded. "They pulled me into the pit, Percy. The things I saw down there..." His voice faltered, and for a moment his vision went completely dark, and the memories pressed closer and closer but he could not break down now, not here.

Hazel had been talking, but now she stopped. Everyone was staring at him. Hazel passed him his sword – where had she found it? – and he wrapped his fingers around its familiar hilt, but he didn't have the strength to do much more than lean on it.

"Now I understand why Hades hasn't been able to close the doors," he said. "Even the gods don't go into Tartarus. Even the god of death, Thanatos himself, wouldn't go near that place."

"So let me guess," said Leo. "We'll have to go there."

Nico shook his head, inwardly marvelling. "It's impossible. I'm the son of Hades, and even I barely survived. Gaia's forces overwhelmed me instantly. They're so powerful down there... no demigod would stand a chance. I almost went insane." Maybe he was.

Percy was looking at him with pity and sadness and shock, perhaps more tenderly than he'd ever looked at Nico before. "Then we'll sail for Epirus," he suggested. "We'll just close the gates on this side."

"I wish it were that easy," Nico said. "The doors would have to be controlled on both sides to be closed. It's like a double seal. Maybe, just maybe, all seven of you working together could defeat Gaia's forces on the mortal side, at the House of Hades. But unless you had a team fighting simultaneously on the Tartarus side, a team powerful enough to defeat a legion of monsters in their home territory—"

"There has to be a way," Jason said, sounding more wishful than confident.

The ship was descending towards a palatial building. Percy glanced down and his eyes darkened. "We'll figure out the Tartarus problem later. Is that the Emmanuel Building?"

Leo nodded. "Bacchus said something about the parking lot in the back? Well, there it is. What now?"

"We have to get her out," Percy said. Nico had only seen an expression like that, all barely-controlled fear and fierce protectiveness, once before: on Annabeth's face the last time he'd seen her in December, when she'd begged him to help her look for Percy.

"Well, yeah," said Leo. "But, uh... there's a parking lot in the way."

"Bacchus said something about breaking through," said Percy. "Coach, you still got ammo for those ballistae?"

Nico hadn't really noticed the satyr before: unlike Grover Underwood, he was middle-aged, with much larger horns and goat legs that he made no attempt to hide. He was grinning crazily. "I thought you'd never ask."

As the satyr ran for the ballistae, Nico frowned. "Annabeth... she's down there? What's she doing?"

"She's been on a solo quest," Hazel explained. "Following the Mark of Athena."

Nico blinked. The words sounded familiar... he thought he'd spoken to the ghost of a demigod child of Athena about this, long ago, but the details eluded him. "What is that?"

"It's like a trail under the city of Rome," said Piper. "It leads to the Athena Parthenos."

"The lost statue in the Parthenon?" Nico's head was spinning. "It's in Rome? But why do you need it?"

Hazel took his hand. "Because the Greek and Roman camps are at war," she said quietly. "The legion is marching on Camp Half-Blood right now. And we think the statue is the only thing that can heal the rift."

"War," Nico repeated hazily. "But... you're all working together – how – and surely Reyna would never be so rash—"

Jason made a growling sound in his throat. "It's not Reyna who's pushing for war," he said. "It's Octavian. If I ever get back to Camp Jupiter, I swear—"

He was interrupted by a whoop from the satyr as the ship's ballistae fired. Beside him, Percy grinned. Leo manoeuvred the Argo II into the gaping new hole in the car park as cars tumbled through.

Percy ran to the side of the ship as they descended into a huge underground cavern. "Annabeth!" he called.

"Here!" The response was little more than a sob.

Nico and the others stared around in astonishment as the ship hovered to a stop about forty feet from the floor. Only Percy moved, sliding down the rope ladder with almost inhuman speed and running over to where Annabeth Chase was standing, staring into a dark hole in the floor. More astonishing, though, was the gigantic statue of Athena filling the cavern with warmth and light. Nico had seen the goddess before, and her ivory face was a perfect likeness. Her robes gleamed purest gold, and she held out a life-sized statue of the goddess Nike in one hand.

"She's beautiful," Piper breathed.

"Come on," Jason murmured, and they followed Percy down the rope ladder.

Percy had reached Annabeth. She hid her face in his chest and burst into tears. "It's okay," Percy was saying, voice low and soothing. "We're together."

Nico took a deep breath, trying to ignore the sharp pain in his chest.

"Your leg," said Piper, reaching out to touch a bubble-wrapped cast around Annabeth's ankle. "Oh, Annabeth, what happened?"

It was, for sure, an impressive story. Nico knew he would never have had the courage to inch across a gaping chasm on a woven bridge, nor would he have survived Annabeth's encounter with the ghostly followers of Mithras. And the monster waiting for her at the statue had been Arachne herself. Nico wasn't even afraid of spiders, and he couldn't imagine how poor Annabeth had faced the monster.

As she talked, he looked around the cavern. It was littered with spider silk; some was trailing from Annabeth's legs and arms, too, and holding together the cracked floor. This cavern was unstable. He wondered whether removing the statue would even be safe.

"Well, it might take some rearranging," Leo was saying, "but I think we can fit her through the bay doors in the stable. If she sticks out of the end, I might have to wrap a flag around her feet or something."

Annabeth shuddered. "What about you guys? What happened with the giants?"

Oh... Nico did not want to listen to this part of the story. He kept his gaze fixed on the statue as Percy explained about the fight with the giants and their conversation aboard the Argo II. Annabeth was giving him that same pitying, half-scared look, as though he was a wounded wild creature who would bite if not handled gently.

"So the mortal side is in Epirus," she said. "At least that's somewhere we can reach."

"But the other side is the problem," said Nico. "Tartarus." Now he wanted to keep saying the name, over and over again, to prove to himself that he wasn't afraid. (But he was afraid.)

The hole behind them exhaled a cold blast of air as he spoke. Nico fell suddenly silent. This hole... it led there. It led to the pit. And the only thing keeping him from falling in was a floor full of cracks, held together with spider webs. He was feeling dizzy again, but this time with fear.

As if following his thoughts, the chamber groaned and the Athena Parthenos tilted ominously. Annabeth paled. "Secure it!"

"Zhang!" Leo cried. "Get me to the helm, quick! The coach is up there alone."

Frank nodded and stretched out his arms. His fingers sharpened into claws. Feathers sprouted along the length of his arms and back, and his nose narrowed to a wicked beak. He was... a giant eagle. Since when had he been able to do that?

Although Nico was gaping, none of the others seemed to see anything out of the ordinary. Jason wrapped his arm around Piper's waist, said, "Back for you guys in a sec," and then shot into the air. Percy gripped Annabeth's hand tightly and led her further away from the edge of the pit.

"This floor won't last!" said Hazel. "The rest of us should get to the ladder." She lunged for the rope ladder and then turned back to gesture at Nico, who stumbled after her. His chest felt tight and his vision was washed in red. What if... what if he didn't make it?

He'd gone nearly blind by the time he reached the ladder, but at last his hand closed on rough rope and he let out a shuddering breath. Tiny tremors were racking his whole body.

"Her ankle!" Hazel shouted from just above him. "Cut it! Cut it!"

Nico looked over his shoulder. Annabeth had fallen flat on her face, being dragged backwards by a rope of silk wrapped around her bad leg. The spider was still there.

He hobbled back towards Percy, who was clutching Annabeth's hands, but he was still moving painfully slowly and Hazel, behind him, had got her spatha entangled with the rope ladder. Nico was the only one close enough to help, but he couldn't move fast enough.

"Help them!" Hazel screamed, but over the din of the others trying to secure the statue, nobody heard her.

He reached the edge of the pit just as Percy and Annabeth tumbled over. Shaking, Nico peered over the edge. Percy had caught onto a tiny ledge about fifteen feet below the edge. Annabeth dangled helplessly beneath him, only his hand keeping her from falling into the void.

There was a high-pitched whining noise in his head, and he had to fight to stop frightened tears spilling out. He couldn't go back. He was so close to the pit, but he couldn't go back. He would die before he entered that place again. Shuddering, he stretched out his hand, but Percy was much to far away to reach him.

Percy stared up at Nico, eyes wide and bright with fear, and then down at Annabeth again. "Percy, let me go," she gasped. "You can't pull me up."

He could do it. If he let go of Annabeth, Percy was strong enough to pull himself onto the ledge, and then Nico could reach across the distance to him. He could do it. But of course he wouldn't.

"Never," he said, his voice trembling with effort. He tilted his head back to look up again. Nico had known Percy Jackson for some three years now, and in all that time he'd never seen despair and determination mingle so fiercely in his sea-green eyes. "The other side, Nico!" he called. "We'll see you there. Understand?"

Nico did, but he didn't want to. He thought his heart might tear itself in two. "But—"

"Lead them there!" Percy shouted. His eyes sparkled with intensity. "Promise me!"

Nico didn't want to say it. He didn't want the words to come out of his mouth. But it was Percy and Nico could not refuse him, could not argue when those eyes were boring into him as though he were the only person in the world, and so he said, "I – I will."

Percy looked at Annabeth. "We're staying together," he said. "You're not getting away from me. Never again."

Tears were running freely down Annabeth's face, but her voice was steady. "As long as we're together," she said.

Nico watched, his hand still extended uselessly below him, as Percy let go of his tiny ledge, and he and Annabeth were swallowed by the darkness.

He could not move. He could not breathe. Perhaps part of it was shock paralysing his bones, but it was more than that. The force of the Underworld tugged at him, hungry. Demanding. The pit had not been happy that he'd escaped it. The pit wanted him back. And he knew, with a sudden cold certainty, that he was going back there, fighting was useless and resistance was pointless because the pit wanted him back to finish its game and the pit always got its wish. But he could not go back. He had a promise to keep.

Come back, the pit seemed to purr in his mind.

"Nico!" Hazel screamed. And then she was beside him, her hand warm and tight around his wrist, and she was forcing him to run as chunks of ceiling fell ahead and behind them and the floor of the ancient cavern crumbled into the pit.

He couldn't really run, but Hazel was pulling him onward, so fast that his lungs burned in protest, and then they slammed into the side of the ship and clung to the edge of the rope ladder for their lives.

"Percy," Hazel moaned. "Percy and Annabeth..."

"They're gone," Nico choked. His sister gave a sob.

The floor was giving way completely. Only a few seconds more, and they would both fall, rope ladder or no – and then there was a pair of firm hands on his shoulders, and Nico went completely limp as the sky seemed to fall towards him and the ladder slipped from his numb fingers, and then Jason Grace set him down on the ship's deck. Beside him, a giant eagle landed on the deck with Hazel in its claws and turned back into Frank.

"Go, Leo!" Hazel cried, and at the helm of the ship the dragon figurehead roared. The ship soared out of the cavern seconds before the roof caved in.

"Where are they?" Piper demanded, gripping her bronze dagger.

Nico's legs gave way and folded beneath him. He sank down onto the floor. "They fell," he said. "Into... into the pit."

Jason, Frank, Piper and Hazel all stared at him. Nico didn't want to meet their gazes. He stared at his knees, hollow and desolate. He was gone.

The ship settled on a hill just outside Rome. Leo ran over, scanning the group, paling as he came up two short. "Percy and Annabeth?"

"We were too late," Jason said dully. Leo shook his head.

"We have to go back there," Hazel said. "Maybe we'll find them."

"Hazel..." Nico trailed off. He'd seen them fall. He knew they were gone. But he was the only one.

Frank turned into an eagle again, and Hazel clambered onto his back. "I'll come, too," Jason offered, and he flew off behind them.

Nico looked up. Piper and Leo were the only other demigods on the ship – the two he knew least well. He realised he didn't even know who their godly parents were. Leo kept casting him nervous looks as they talked quietly with each other. He was afraid of Nico. Well, nothing new there.

Nico thought of how the campers at Camp Half-Blood had cast him those uneasy sideways looks if he ever appeared beside them or came to sit at their table at dinnertime, even after the Battle of Manhattan. Had they thought he didn't notice them? Perhaps they thought children of the Underworld didn't have feelings, anyway.

Percy hadn't been like that. He'd always greeted Nico with a smile – but it had been too painful, being with Percy once he and Annabeth started dating.

And now Percy was gone.

Hazel, Frank and Jason were back sooner than Nico expected. The boys' faces were grim. Hazel looked like she had been crying. She slid out of Frank's grasp and sat down beside Nico, which made him feel a little better.

"The cavern's been buried," Jason said wearily. "We tried to dig through the rubble, but... but it's just gone."

"None of the mortals were hurt," Frank added. "And the entrance to the pit is sealed off. But..."

Piper stared at the huge statue hanging behind the ship, still tangled in the grappling ropes. "Annabeth saved the statue," she said, voice trembling. "We have to take care of it. Come on."

The others stumbled after her like sleepwalkers, but they managed to load the statue into the ship's bay. Nico wasn't sure, but he thought he saw Frank turn into an elephant at one point. Since when did klutzy Zhang have all these cool powers?

Hazel had stayed sitting beside him. For a few moments they were quiet. Then Hazel spoke. "Are they dead?" Her voice was very low.

Nico had already asked himself that. "No," he said. "I don't think they are. Do you?"

She glanced at him uncertainly. Hazel had never had many powers over the dead. Her sphere was riches, not death. But she closed her eyes for a moment, before saying, "I don't think so."

"You'd know if they were," Nico told her. "When it's someone you know... well, you'd know if they died." He thought of the day three years ago when he'd felt a sharp, stabbing pain in his chest. Nothing serious, or prolonged, and he hadn't thought much of it at the time. But a few days later Percy Jackson had come back to camp and told him his sister was dead.

Hazel folded her fingers around his, and he let himself lean into his sister's shoulder. She wasn't Bianca, but that didn't mean he couldn't love her.

"I was so afraid," she murmured now. "The whole time... It's – it's awful that Percy and Annabeth are gone, but I'm glad you're okay."

"I'm not," Nico said, before he could stop himself. Then he took a breath. "I'll be fine, though. I promised Percy—" the name was difficult, but he kept his voice steady – "I'd lead you to Epirus. You'll need my help to get to the Doors of Death. We can meet them there."

"You think they can survive there?" Hazel looked at him as though he was made of silk and feathers and the slightest breath would blow him away.

"If anyone can, they can," Nico said, hoping he sounded more confident than he felt.

The rest of the crew, and the satyr called Coach, were making their way back towards them. Hazel stood and extended a hand to Nico. He took it, and she wrapped her arms suddenly around him.

Nico didn't try to pull away, for once. He hid his face in his sister's shoulder and finally – finally – let the tears come.