Frank followed his gaze. The Americans’ faces were angry and confused, like they were sleepwalking through a very annoying nightmare.

“Leo Valdez,” called the guy in the ROMA shirt. His voice had changed. It was hollow and metallic. He spoke English as if it was a second language. “We meet again.”

All three tourists blinked, and their eyes turned solid gold.

Frank yelped. “Eidolons!”

The manatees clenched their beefy fists. Normally, Leo wouldn’t have worried about getting murdered by overweight guys in floppy hats, but he suspected the eidolons were dangerous even in those bodies, especially since the spirits wouldn’t care whether their hosts survived or not.

“They can’t fit down the hole,” Leo said.

“Right,” Frank said. “Underground is sounding really good.”

He turned into a snake and slithered over the edge. Leo jumped in after him while the spirits began to wail above, “Valdez! Kill Valdez!”

Chapter 38

One problem solved: the hatch above them closed automatically, cutting off their pursuers. It also cut off all light, but Leo and Frank could deal with that. Leo just hoped they didn’t need to get out the same way they came in. He wasn’t sure he could open the tile from underneath.

At least the possessed manatee dudes were on the other side. Over Leo’s head, the marble floor shuddered, like fat touristy feet were kicking it.

Frank must have turned back to human form. Leo could hear him wheezing in the dark.

“What now?” Frank asked.

“Okay, don’t freak,” Leo said. “I’m going to summon a little fire, just so we can see.”

“Thanks for the warning.”

Leo’s index finger blazed like a birthday candle. In front of them stretched a stone tunnel with a low ceiling. Just as Hazel had predicted, it slanted down, then leveled out and went south.

“Well,” Leo said. “It only goes in one direction.”

“Let’s find Hazel,” Frank said.

Leo had no argument with that suggestion. They made their way down the corridor, Leo going first with the fire. He was glad to have Frank at his back, big and strong and able to turn into scary animals in case those possessed tourists somehow broke through the hatch, squeezed inside, and followed them. He wondered if the eidolons might just leave those bodies behind, seep underground, and possess one of them instead.

Oh, there’s my happy thought for the day! Leo scolded himself.

After a hundred feet or so, they turned a corner and found Hazel. In the light of her golden cavalry sword, she was examining a door. She was so engrossed, she didn’t notice them until Leo said, “Hi.”

Hazel whirled, trying to swing her spatha. Fortunately for Leo’s face, the blade was too long to wield in the corridor.

“What are you doing here?” Hazel demanded.

Leo gulped. “Sorry. We ran into some angry tourists.” He told her what had happened.

She hissed in frustration. “I hate eidolons. I thought Piper made them promise to stay away.”

“Oh…” Frank said, like he’d just had his own daily happy thought. “Piper made them promise to stay off the ship and not possess any of us. But if they followed us, and used other bodies to attack us, then they’re not technically breaking their vow.…”

“Great,” Leo muttered. “Eidolons who are also lawyers. Now I really want to kill them.”

“Okay, forget them for now,” Hazel said. “This door is giving me fits. Leo, can you try your skill with the lock?”

Leo cracked his knuckles. “Stand aside for the master, please.”

The door was interesting, much more complicated than the Roman numeral combination lock above. The entire door was coated in Imperial gold. A mechanical sphere about the size of a bowling ball was embedded in the center. The sphere was constructed from five concentric rings, each inscribed with zodiac symbols—the bull, the scorpion, et cetera—and seemingly random numbers and letters.

“These letters are Greek,” Leo said in surprise.

“Well, lots of Romans spoke Greek,” Hazel said.

“I guess,” Leo said. “But this workmanship…no offense to you Camp Jupiter types, but this is too complicated to be Roman.”

Frank snorted. “Whereas you Greeks just love making things complicated.”

“Hey,” Leo protested. “All I’m saying is this machinery is delicate, sophisticated. It reminds me of…” Leo stared at the sphere, trying to recall where he’d read or heard about a similar ancient machine. “It’s a more advanced sort of lock,” he decided. “You line up the symbols on the different rings in the right order, and that opens the door.”

“But what’s the right order?” Hazel asked.

“Good question. Greek spheres…astronomy, geometry…” Leo got a warm feeling inside. “Oh, no way. I wonder…What’s the value of pi?”

Frank frowned. “What kind of pie?”

“He means the number,” Hazel guessed. “I learned that in math class once, but—”

“It’s used to measure circles,” Leo said. “This sphere, if it’s made by the guy I’m thinking of…”

Hazel and Frank both stared at him blankly.

“Never mind,” Leo said. “I’m pretty sure pi is, uh, 3.1415 blah blah blah. The number goes on forever, but the sphere has only five rings, so that should be enough, if I’m right.”

“And if you’re not?” Frank asked.

“Well, then, Leo fall down, go boom. Let’s find out!”

He turned the rings, starting on the outside and moving in. He ignored the zodiac signs and letters, lining up the correct numbers so they made the value of pi. Nothing happened.

“I’m stupid,” Leo mumbled. “Pi would expand outward, because it’s infinite.”

He reversed the order of the numbers, starting in the center and working toward the edge. When he aligned the last ring, something inside the sphere clicked. The door swung open.

Leo beamed at his friends. “That, good people, is how we do things in Leo World. Come on in!”

“I hate Leo World,” Frank muttered.

Hazel laughed.

Inside was enough cool stuff to keep Leo busy for years. The room was about the size of the forge back at Camp Half-Blood, with bronze-topped worktables along the walls, and baskets full of ancient metalworking tools. Dozens of bronze and gold spheres like steampunk basketballs sat around in various stages of disassembly. Loose gears and wiring littered the floor. Thick metal cables ran from each table toward the back of the room, where there was an enclosed loft like a theater’s sound booth. Stairs led up to the booth on either side. All the cables seemed to run into it. Next to the stairs on the left, a row of cubbyholes was filled with leather cylinders—probably ancient scroll cases.

Leo was about to head toward the tables when he glanced to his left and nearly jumped out of his shoes. Flanking the doorway were two armored manikins—like skeletal scarecrows made from bronze pipes, outfitted with full suits of Roman armor, shield and sword.

“Dude.” Leo walked up to one. “These would be awesome if they worked.”

Frank edged away from the manikins. “Those things are going to come alive and attack us, aren’t they?”

Leo laughed. “Not a chance. They aren’t complete.” He tapped the nearest manikin’s neck, where loose copper wires sprouted from underneath its breastplate. “Look, the head’s wiring has been disconnected. And here, at the elbow, the pulley system for this joint is out of alignment. My guess? The Romans were trying to duplicate a Greek design, but they didn’t have the skill.”

Hazel arched her eyebrows. “The Romans weren’t good enough at being complicated, I suppose.”

“Or delicate,” Frank added. “Or sophisticated.”

“Hey, I just call it like I see it.” Leo jiggled the manikin’s head, making it nod like it was agreeing with him. “Still…a pretty impressive try. I’ve heard legends that the Romans confiscated the writings of Archimedes, but—”

“Archimedes?” Hazel looked baffled. “Wasn’t he an ancient mathematician or something?”

Leo laughed. “He was a lot more than that. He was only the most famous son of Hephaestus who ever lived.”

Frank scratched his ear. “I’ve heard his name before, but how can you be sure this manikin is his design?”

“It has to be!” Leo said. “Look, I’ve read all about Archimedes. He’s a hero to Cabin Nine. The dude was Greek, right? He lived in one of the Greek colonies in southern Italy, back before Rome got all huge and took over. Finally the Romans moved in and destroyed his city. The Roman general wanted to spare Archimedes, because he was so valuable—sort of like the Einstein of the ancient world—but some stupid Roman soldier killed him.”

“There you go again,” Hazel muttered. “Stupid and Roman don’t always go together, Leo.”

Frank grunted agreement. “How do you know all this, anyway?” he demanded. “Is there a Spanish tour guide around here?”

“No, man,” Leo said. “You can’t be a demigod who’s into building stuff and not know about Archimedes. The guy was seriously elite. He calculated the value of pi. He did all this math stuff we still use for engineering. He invented a hydraulic screw that could move water through pipes.”

Hazel scowled. “A hydraulic screw. Excuse me for not knowing about that awesome achievement.”

“He also built a death ray made of mirrors that could burn enemy ships,” Leo said. “Is that awesome enough for you?”

“I saw something about that on TV,” Frank admitted. “They proved it didn’t work.”

“Ah, that’s just because modern mortals don’t know how to use Celestial bronze,” Leo said. “That’s the key. Archimedes also invented a massive claw that could swing on a crane and pluck enemy ships out of the water.”

“Okay, that’s cool,” Frank admitted. “I love grabber-arm games.”

“Well, there you go,” Leo said. “Anyway, all his inventions weren’t enough. The Romans destroyed his city. Archimedes was killed. According to legends, the Roman general was a big fan of his work, so he raided Archimedes’s workshop and carted a bunch of souvenirs back to Rome. They disappeared from history, except…” Leo waved his hands at the stuff on the tables. “Here they are.”

“Metal basketballs?” Hazel asked.

Leo couldn’t believe that they didn’t appreciate what they were looking at, but he tried to contain his irritation. “Guys, Archimedes constructed spheres. The Romans couldn’t figure them out. They thought they were just for telling time or following constellations, because they were covered with pictures of stars and planets. But that’s like finding a rifle and thinking it’s a walking stick.”

“Leo, the Romans were top-notch engineers,” Hazel reminded him. “They built aqueducts, roads—”