Will was relieved to have his feet on something other than the‌

slimy stone steps, even if it was the banks of the Styx. The air here was thick with … something; he wasn’t sure what, but at

least they were out of that dark tunnel.

Nico had been right about the Underworld having some light. Its sky –

could he call it a sky? – was a glowing hazy red, punctuated with flashes of orange and veins of dark shadows. Where was the light coming from? The air seemed polluted, even worse than he’d experienced in cities like

Houston or Los Angeles while touring with his mom. In the distance, across the river, towering stone walls with black battlements stretched as far as he could see, blocking off access to … the land of the dead? Hades’s home?

Will didn’t want to find out. The fortress was terrifying.

‘Welcome to the Underworld,’ Nico said, sweeping his arm towards the horizon like he was showing off something he was proud of. He actually looked happy to be here.

Well, this was his home, technically.

Will couldn’t escape the sense of dread crawling over his skin as he peered around. He had a confused feeling that he had been here before … But he also didn’t remember how he’d got here. His instincts told him this was all wrong. He should run. But he had to endure it … He had to try if this quest was going to succeed.

‘Impressive,’ he said weakly. ‘Where do we go now?’

‘This way.’ Nico tucked his sword away and ran off to the right, bounding over the boulders that jutted along the river’s edge.

Will hesitated. He was enjoying not moving, and his limbs felt like lead.

How did Nico have so much energy? Will wondered if this was what he

looked like to Nico in the world above.

‘Hey, wait up!’ Will called out, pulling the straps on his knapsack to keep it tight against his back.

He chased after Nico, who moved like a mountain goat over the jagged rocks. Will wasn’t sure that Nico had even heard him yell, as the roar of the River Styx was impossibly loud here, the churn of the rapids booming off the cavern walls. Nico stopped at the top of a boulder, where the River Styx widened into a swirling back eddy five metres below.

Nico turned towards Will with a crooked smile, waved, and then –‘Nico, no!’

Nico jumped in.

By the time Will made it to the boulder top, Nico’s head was bobbing along in the middle of the river. He was doggy-paddling along in the inky water, grinning as if he was enjoying his dip, which … gods, wasn’t that

impossible? Will remembered Percy talking about his brief plunge into the Styx: how it was like acid to the human soul, eating away your very identity. It had almost destroyed him in a matter of seconds. Was Nico

somehow immune to the river’s effects?

‘Nico!’ he screamed, running along the rocky bank as fast as he could.

Why hadn’t Nico talked to Will about this? Why did he always have so many secrets? Didn’t he know by now that he could trust his own boyfriend?

The muscles in Will’s legs screamed at him to stop, and despair ripped through him. He couldn’t keep up with the raging and turbulent current; Nico was getting further and further away, heading towards the next set of cataracts. Didn’t Nico see the danger?

His chest burning, he managed to scream Nico’s name one more time. Before Nico plunged over the edge of the falls.

Will’s cry was lost in the terrible sound of the Styx. He forced himself to keep going until he stood at the top of the cataract, a lower tier of the

Underworld stretching out impossibly far beneath him. He scanned the

water, terrified that he might see Nico’s lifeless form, but in the pool below, illuminated by a purple glow, Nico was bobbing along just fine.

Will was furious. What was Nico thinking?

Nico glanced up, saw him and waved his sword like a racing flag. ‘Just jump in!’ he yelled, his voice strangely close, as if he were standing right next to Will. ‘The water’s fine!’

These words made even less sense to Will than what he had just witnessed.

The water’s fine?

Which got Will thinking … Had he ever seen Nico swimming? Did Nico even know how? In Will’s exhaustion and terror, an absurd image popped into his head: Nico wearing one of those old-timey one-piece men’s

swimsuits while floating in an inner tube. In Will’s frazzled state of mind, that seemed hysterically funny. Too bad no one else was around for Will to share it with.

‘Don’t hold me back!’ Nico shouted up at him. ‘We have to keep moving.’

‘What’s got into your head, Nico?’ he asked softly, not expecting Nico to hear him.

‘Don’t you want to save Bob?’ Nico yelled. ‘Or are you giving up on our quest already? I knew you would.’

‘What?’ Will felt punched in the gut. Nausea threatened to overwhelm him. ‘No, of course not! But what am I supposed to do? Is this part of the plan?’

‘Jump in,’ said Nico. ‘You’ll be fine. I promise.’

Will had done any number of ridiculous things since learning he was a son of Apollo. Sure, demigods possessed abilities that pushed the limits of what human bodies were capable of. He’d seen incredible leaps, tumbles,

tackles and other feats over the years. At the same time, demigods were all still heartbreakingly mortal, and they could definitely get seriously hurt. As one of the main field medics in camp, Will had seen it firsthand.

And in no way was he prepared to jump into a soul-destroying, toxic river of damnation.

‘Stop giving up on me,’ said Nico, and this time Will swore he could feel his boyfriend’s breath on his neck. ‘Come on! Don’t be a coward.’

That comment sent a burst of anger through Will. How could Nico be so cruel? Why would he ever think of Will as a coward?

A new theory started to coil around the base of Will’s brain: what if the Underworld was already changing Nico?

All that talk from Percy and Annabeth …

What was it Percy had said? I practically lost myself in that place. He’d meant Tartarus, but what if that process had started happening even before? What if Nico didn’t even realize how much he was changing? Will had to get him out of that water before it was too late, whatever the cost.

He flipped his knapsack around so that it was over his chest, clasped it tightly and jumped.

Will had braced himself for a jolt of cold water.

Instead, the River Styx burned. Even that was an understatement. As pain ripped through his body, his mind drifted to the memory of sitting under a tattoo gun, the needle pressing into his skin on his pectoral as his mom held his hand. She had taken him to the shop and helped him choose a design to honour his father. But once the process had begun, he’d been surprised that the sensation had felt like burning, like he was skinning his knee from a fall over and over again.

Except the River Styx was a billion tattoo guns running over every inch of his body, and the ink was made of acid, and also everything was on fire, including the fire.

Yes, he decided as he bobbed to the surface, gasping for air, down here, the fire is on fire.

His skin felt like it was melting off, and he wished he hadn’t filled his knapsack with so much stuff. It was hard enough to swim without that extra weight.

His head went under, and a mouthful of the River Styx actually went down his throat.

If that water felt awful all over the outside of his body, it was even worse on the inside. He kicked as ferociously as he could, his muscles aching from the overexertion, and his head broke the surface again. His throat burned so badly even breathing hurt. He twisted around, looking for Nico. Where had he gone?

‘Hurry up, slowpoke.’ Nico’s voice wafted past Will’s left ear.

Will turned. His vision was hazy, but he saw a purple glow moving across the shoreline. How had Nico got out of the water so fast?

Will flung his arms towards the bank, then paddled frantically until the water was shallow enough for him to stand in. By the time he flopped onto his back on the rocky riverbank, trembling and wheezing, he felt like he’d just taken a long bath in his mom’s favourite ghost-pepper salsa. Will imagined he could bottle Styx water and sell it as the hottest hot sauce in

the world. Mr D would probably be his celebrity sponsor for a hefty percentage.

He laughed. He laughed because everything hurt, because he shouldn’t be alive, because he was delirious from the pain and total absurdity of plunging into the River Styx.

Wait. Was he … invulnerable now? Wasn’t that what happened if you

survived a dip in the Styx? That couldn’t be right. It couldn’t be that easy.

He rolled over and pushed himself up to his hands and knees. He

coughed out more acidic black water, which burned on its way out, too. Well, at least it was consistent.

‘Nico,’ he croaked, swaying as he stood up. ‘Nico, where are you?’ No one was there.

Then Will turned and glimpsed the familiar purple glow disappearing behind an outcrop of stalagmites.

He tried to yell ‘Nico, stop!’ but his lungs were on fire. His skin felt … Oh, gods, was this what a sunburn was like? Being a child of Apollo meant he had never got one, and if it was anything similar to this sensation, he had immense sympathy for all the lobster-red campers he’d seen and healed over the years.

The purple glow was getting dimmer in the distance.

‘You’re just slowing me down,’ his boyfriend’s voice whispered in his ear.

How was this possible? Was Will’s mind dissolving? ‘I won’t, Nico,’ he said, sobbing. ‘I promise.’

‘You already are.’

Will watched in despair as the faint purple glow slipped into the shadows and disappeared.

He crumpled to his knees, tears prickling his eyes. This wasn’t happening. This couldn’t happen. Nico would never do something like this to him!

‘Nico!’ he cried out. ‘Come back!’

But this time Nico didn’t answer. Behind Will, the Styx rushed past.

Will’s skin and clothes steamed. Will kept staring into the darkness, hoping to see that purple glow reappear.

Then a heavy shadow fell over him. Will didn’t have the strength to fight as it enveloped him like a burial cloth.