Leo hated to give away a perfectly good Valdezinator for a wildflower, but he saw no other choice. 'You drive a hard bargain, Music Man.'

They made the trade.

'Excellent!' Apollo turned the levers of the Valdezinator, which made a sound like a car engine on a cold morning. 'Hmm ... perhaps it'll take some practice, but I'll get it! Now let us find your friends. The sooner you leave, the better!'

Hazel and Frank waited at the Delos docks. Artemis was nowhere in sight.

When Leo turned to tell Apollo goodbye, the god was gone, too.

'Man,' Leo muttered, 'he was really anxious to practice his Valdezinator.'

'His what?' Hazel asked.

Leo told them about his new hobby as a genius inventor of musical funnels.

Frank scratched his head. 'And in exchange you got a daisy?'

'It's the final ingredient to cure death, Zhang. It's a super daisy! How about you guys? Learn anything from Artemis?'

'Unfortunately, yes.' Hazel gazed across the water, where the Argo II bobbed at anchor. 'Artemis knows a lot about missile weapons. She told us Octavian has ordered some ... surprises for Camp Half-Blood. He's used most of the legion's treasure to purchase Cyclopes-built onagers.'

'Oh, no, not onagers!' Leo said. 'Also, what's an onager?'

Frank scowled. 'You build machines. How can you not know what an onager is? It's just the biggest, baddest catapult ever used by the Roman army.'

'Fine,' Leo said. 'But onager is a stupid name. They should've called them Valdezapults.'

Hazel rolled her eyes. 'Leo, this is serious. If Artemis is right, six of these machines will be rolling into Long Island tomorrow night. That's what Octavian has been waiting for. At dawn on August first, he'll have enough firepower to completely destroy Camp Half-Blood without a single Roman casualty. He thinks that'll make him a hero.'

Frank muttered a Latin curse. 'Except he's also summoned so many monstrous "allies" that the legion is completely surrounded by wild centaurs, tribes of dog-headed cynocephali, and who knows what else. As soon as the legion destroys Camp Half-Blood, the monsters will turn on Octavian and destroy the legion.'

'And then Gaia rises,' Leo said. 'And bad stuff happens.'

In his head, gears turned as the new information clicked into place. 'All right ... this just makes my plan even more important. Once we get this physician's cure, I'm going to need your help. Both of you.'

Frank glanced nervously at the cursed yellow daisy. 'What kind of help?'

Leo told them his plan. The more he talked, the more shocked they looked, but when he was done neither of them told him he was crazy. A tear glistened on Hazel's cheek.

'It has to be this way,' Leo said. 'Nike confirmed it. Apollo confirmed it. The others would never accept it, but you guys ... you're Romans. That's why I wanted you to come to Delos with me. You get the whole sacrifice thing doing your duty, jumping on your sword.'

Frank sniffled. 'I think you mean falling on your sword.'

'Whatever,' Leo said. 'You know this has to be the answer.'

'Leo ...' Frank choked up.

Leo himself wanted to cry like a Valdezinator, but he kept his cool. 'Hey, big guy, I'm counting on you. Remember you told me about that conversation with Mars? Your dad said you'd have to step up, right? You'd have to make the call nobody else was willing to make.'

'Or the war would go sideways,' Frank remembered. 'But still '

'And Hazel,' Leo said. 'Crazy Mist-magicky Hazel, you've got to cover for me. You're the only one who can. My great-granddad Sammy saw how special you were. He blessed me when I was a baby, because I think somehow he knew you were going to come back and help me. Our whole lives, mi amiga, they've been leading up to this.'

'Oh, Leo ...' She really did burst into tears then. She grabbed him and hugged him, which was sweet until Frank started crying too and wrapped them both in his arms.

That got a little weird.

'Okay, well ...' Leo gently extricated himself. 'So we're in agreement?'

'I hate this plan,' Frank said.

'I despise it,' Hazel said.

'Think how I feel,' Leo said. 'But you know it's our best shot.'

Neither of them argued. Leo kind of wished they had.

'Let's get back to the ship,' he said. 'We have a healer god to find.'

XXXV.

Leo

LEO SPOTTED THE SECRET ENTRANCE IMMEDIATELY.

'Oh, that's beautiful.' He manoeuvred the ship over the ruins of Epidaurus.

The Argo II really wasn't in good shape to fly, but Leo had got her airborne after only one night of work. With the world ending tomorrow morning, he was highly motivated.

He'd primed the oar flaps. He'd injected Styx water into the samophlange. He'd treated Festus the figurehead to his favourite brew thirty-weight motor oil and Tabasco sauce. Even Buford the Wonder Table had pitched in, rattling around belowdecks while his holographic Mini-Hedge yelled, 'GIVE ME THIRTY PUSH-UPS!' to inspire the engine.

Now, at last, they hovered over the ancient temple complex of the healing god Asclepius, where they could hopefully find the physician's cure and maybe also some ambrosia, nectar and Fonzies, because Leo's supplies were running low.

Next to him on the quarterdeck, Percy peered over the railing.

'Looks like more rubble,' he noted.

His face was still green from his underwater poisoning, but at least he wasn't running to the bathroom to upchuck quite so often. Between him and Hazel's seasickness, it had been impossible to find an unoccupied toilet onboard for the past few days.

Annabeth pointed to the disc-shaped structure about fifty yards off their port side. 'There.'

Leo smiled. 'Exactly. See, the architect knows her stuff.'

The rest of the crew gathered around.

'What are we looking at?' Frank asked.

'Ah, Senor Zhang,' Leo said, 'you know how you're always saying, "Leo, you are the only true genius among demigods"?'

'I'm pretty sure I never said that.'

'Well, turns out there are other true geniuses! Because one of them must have made that work of art down there.'

'It's a stone circle,' Frank said. 'Probably the foundation of an old shrine.'

Piper shook her head. 'No, it's more than that. Look at the ridges and grooves carved around the rim.'

'Like the teeth of a gear,' Jason offered.

'And those concentric rings.' Hazel pointed to the centre of the structure, where curved stones formed a sort of bull's-eye. 'The pattern reminds me of Pasiphae's pendant: the symbol of the Labyrinth.'

'Huh.' Leo scowled. 'Well, I hadn't thought of that. But think mechanical. Frank, Hazel ... where did we see concentric circles like that before?'

'The laboratory under Rome,' Frank said.

'The Archimedes lock on the door,' Hazel recalled. 'It had rings within rings.'

Percy snorted. 'You're telling me that's a massive stone lock? It's, like, fifty feet in diameter.'

'Leo might be right,' Annabeth said. 'In ancient times, the temple of Asclepius was like the General Hospital of Greece. Everybody came here for the best healing. Aboveground, it was the size of a major city, but supposedly the real action happened belowground. That's where the high priests had their intensive-care super-magical-type compound, accessed by a secret passage.'

Percy scratched his ear. 'So, if that big round thing is the lock, how do we get the key?'

'Way ahead of you, Aquaman,' Leo said.

'Okay, do not call me Aquaman. That's even worse than water boy.'

Leo turned to Jason and Piper. 'You guys remember the giant Archimedes grabber arm I told you I was building?'

Jason raised an eyebrow. 'I thought you were kidding.'

'Oh, my friend, I never kid about giant grabber arms!' Leo rubbed his hands in anticipation. 'It's time to go fishing for prizes!'

Compared to the other modifications Leo had made to the ship, the grabber arm was a piece of cake. Originally, Archimedes had designed it to pluck enemy ships out of the water. Now Leo found another use for it.

He opened the hull's forward access vent and extended the arm, guided by the console monitor and Jason, who flew outside, yelling directions.

'Left!' Jason called. 'A couple of inches yeah! Okay, down. Keep it coming. You're good.'

Using his trackpad and turntable controls, Leo opened the claw. Its prongs settled around the grooves in the circular stone structure below. He checked the aerial stabilizers and the monitor's video feed.

'Okay, little buddy.' Leo patted the Archimedes sphere embedded in the helm. 'This is all you.'

He activated the sphere.

The grabber arm began to turn like a corkscrew. It rotated the outer ring of stone, which ground and rumbled but thankfully didn't shatter. Then the claw detached, fixed itself around the second stone ring and turned it in the opposite direction.

Standing next to him at the monitor, Piper kissed him on the cheek. 'It's working. Leo, you're amazing.'

Leo grinned. He was about to make a comment about his own awesomeness, then he remembered the plan he had worked out with Hazel and Frank and the fact that he might never see Piper again after tomorrow. The joke sort of died in his throat. 'Yeah, well ... thanks, Beauty Queen.'

Below them, the last stone ring turned and settled with a deep pneumatic hiss. The entire fifty-foot pedestal telescoped downward into a spiral staircase.

Hazel exhaled. 'Leo, even from up here, I'm sensing bad stuff at the bottom of those stairs. Something ... large and dangerous. You sure you don't want me to come along?'

'Thanks, Hazel, but we'll be good.' He patted Piper on the back. 'Me and Piper and Jason we're old pros at large and dangerous.'

Frank held out the vial of Pylosian mint. 'Don't break it.'

Leo nodded gravely. 'Don't break the vial of deadly poison. Man, I'm glad you said that. Never would have occurred to me.'

'Shut up, Valdez.' Frank gave him a bear hug. 'And be careful.'

'Ribs,' Leo squeaked.

'Sorry.'

Annabeth and Percy wished them good luck. Then Percy excused himself to go throw up.

Jason summoned the winds and whisked Piper and Leo down to the surface.

The stairs spiralled downward about sixty feet before opening into a chamber as large as Bunker Nine which is to say, ginormous.

The polished white tiles on the walls and floor reflected the light of Jason's sword so well that Leo didn't need to make a fire. Rows of long stone benches filled the entire chamber, reminding Leo of one of those mega-churches they always advertised back in Houston. At the far end of the room, where the altar would have been, stood a ten-foot-tall statue of pure white alabaster a young woman in a white robe, a serene smile on her face. In one hand she raised a cup, while a golden serpent coiled around her arm, its head poised over the brim as if ready to drink.

'Large and dangerous,' Jason guessed.

Piper scanned the room. 'This must have been the sleeping area.' Her voice echoed a little too loudly for Leo's comfort. 'The patients stayed here overnight. The god Asclepius was supposed to send them a dream, telling them what cure to ask for.'

'How do you know that?' Leo asked. 'Annabeth told you?'

Piper looked offended. 'I know stuff. That statue over there is Hygeia, the daughter of Asclepius. She's the goddess of good health. That's where we get the word hygiene.'

Jason studied the statue warily. 'What's with the snake and the cup?'

'Uh, not sure,' Piper admitted. 'But back in the day this place the Asclepeion was a medical school as well as a hospital. All the best doctor-priests trained here. They would've worshipped both Asclepius and Hygeia.'