Leo was no architect like Annabeth, but he could appreciate the engineering. The Romans had made the dome out of big stone panels, but they’d hollowed out each panel in a square-within-square pattern. It looked cool. Leo figured it also made the dome lighter and easier to support.

He didn’t mention that to his friends. He doubted they would care, but if Annabeth were here, she would’ve spent the whole day talking about it. Thinking about that made Leo wonder how she was doing on her Mark of Athena expedition. Leo never thought he’d feel this way, but he was worried about that scary blond girl.

Hazel stopped in the middle of the room and turned in a circle. “This is amazing. In the old days, the children of Vulcan would come here in secret to consecrate demigod weapons. This is where Imperial gold was enchanted.”

Leo wondered how that worked. He imagined a bunch of demigods in dark robes trying to quietly roll a scorpion ballista through the front doors.

“But we’re not here because of that,” he guessed.

“No,” Hazel said. “There’s an entrance—a tunnel that will lead us toward Nico. I can sense it close by. I’m not sure where.”

Frank grunted. “If this building is two thousand years old, it makes sense there could be some kind of secret passage left over from the Roman days.”

That’s when Leo made his mistake of simply being too good.

He scanned the temple’s interior, thinking: If I were designing a secret passage, where would I put it?

He could sometimes figure out how a machine worked by putting his hand on it. He’d learned to fly a helicopter that way. He’d fixed Festus the dragon that way (before Festus crashed and burned). Once he’d even reprogrammed the electronic billboards in Times Square to read: ALL DA LADIES LUV LEO…accidentally, of course.

Now he tried to sense the workings of this ancient building. He turned toward a red marble altar-looking thing with a statue of the Virgin Mary on the top. “Over there,” he said.

He marched confidently to the shrine. It was shaped sort of like a fireplace, with an arched recess at the bottom. The mantel was inscribed with a name, like a tomb.

“The passage is around here,” he said. “This guy’s final resting place is in the way. Raphael somebody?”

“Famous painter, I think,” Hazel said.

Leo shrugged. He had a cousin named Raphael, and he didn’t think much of the name. He wondered if he could produce a stick of dynamite from his tool belt and do a little discreet demolition; but he figured the caretakers of this place probably wouldn’t approve.

“Hold on…” Leo looked around to make sure they weren’t being watched.

Most of the tour groups were gawking at the dome, but one trio made Leo uneasy. About fifty feet away, some overweight middle-aged dudes with American accents were conversing loudly, complaining to each other about the heat. They looked like manatees stuffed into beach clothes—sandals, walking shorts, touristy T-shirts and floppy hats. Their legs were big and pasty and covered with spider veins. The guys acted extremely bored, and Leo wondered why they were hanging around.

They weren’t watching him. Leo wasn’t sure why they made him nervous. Maybe he just didn’t like manatees.

Forget them, Leo told himself.

He slipped around the side of the tomb. He ran his hand down the back of a Roman column, all the way to the base. Right at the bottom, a series of lines had been etched into the marble—Roman numerals.

“Heh,” Leo said. “Not very elegant, but effective.”

“What is?” Frank asked.

“The combination for a lock.” He felt around the back of the column some more and discovered a square hole about the size of an electrical socket. “The lock face itself has been ripped out—probably vandalized sometime in the last few centuries. But I should be able to control the mechanism inside, if I can…”

Leo placed his hand on the marble floor. He could sense old bronze gears under the surface of the stone. Regular bronze would have corroded and become unusable long ago, but these were Celestial bronze—the handiwork of a demigod. With a little willpower, Leo urged them to move, using the Roman numerals to guide him. The cylinders turned—click, click, click. Then click, click.

On the floor next to the wall, one section of marble tile slid under another, revealing a dark square opening barely large enough to wiggle through.

“Romans must’ve been small.” Leo looked at Frank appraisingly. “You’ll need to change into something thinner to get through here.”

“That’s not nice!” Hazel chided.

“What? Just saying—”

“Don’t worry about it,” Frank mumbled. “We should go get the others before we explore. That’s what Piper said.”

“They’re halfway across the city,” Leo reminded him. “Besides, uh, I’m not sure I can close this hatch again. The gears are pretty old.”

“Great,” Frank said. “How do we know it’s safe down there?”

Hazel knelt. She put her hand over the opening as if checking the temperature. “There’s nothing alive…at least not for several hundred feet. The tunnel slants down, then levels out and goes south, more or less. I don’t sense any traps…”

“How can you tell all that?” Leo asked.

She shrugged. “Same way you can pick locks on marble columns, I guess. I’m glad you’re not into robbing banks.”

“Oh…bank vaults,” Leo said. “Never thought about that.”

“Forget I said anything.” Hazel sighed. “Look, it’s not three o’clock yet. We can at least do a little exploring, try to pinpoint Nico’s location before we contact the others. You two stay here until I call for you. I want to check things out, make sure the tunnel is structurally sound. I’ll be able to tell more once I’m underground.”

Frank scowled. “We can’t let you go by yourself. You could get hurt.”

“Frank, I can take care of myself,” she said. “Underground is my specialty. It’s safest for all of us if I go first.”

“Unless Frank wants to turn into a mole,” Leo suggested. “Or a prairie dog. Those things are awesome.”

“Shut up,” Frank mumbled.

“Or a badger.”

Frank jabbed a finger at Leo’s face. “Valdez, I swear—”

“Both of you, be quiet,” Hazel scolded. “I’ll be back soon. Give me ten minutes. If you don’t hear from me by then…Never mind. I’ll be fine. Just try not to kill each other while I’m down there.”

She dropped down the hole. Leo and Frank blocked her from view as best they could. They stood shoulder to shoulder, trying to look casual, like it was completely natural for two teenaged guys to hang around Raphael’s tomb.

Tour groups came and went. Most ignored Leo and Frank. A few people glanced at them apprehensively and kept walking. Maybe the tourists thought they would ask for tips. For some reason, Leo could unnerve people when he grinned.

The three American manatees were still hanging out in the middle of the room. One of them wore a T-shirt that said ROMA, as if he’d forget what city he was in if he didn’t wear it. Every once in a while, he would glance over at Leo and Frank like he found their presence distasteful.

Something about that dude bothered Leo. He wished Hazel would hurry up.

“She talked to me earlier,” Frank said abruptly. “Hazel told me you figured out about my lifeline.”

Leo stirred. He’d almost forgotten Frank was standing next to him.

“Your lifeline…oh, the burning stick. Right.” Leo resisted the urge to set his hand ablaze and yell: Bwah ha ha! The idea was sort of funny, but he wasn’t that cruel.

“Look, man,” he said. “It’s cool. I’d never do anything to put you in danger. We’re on the same team.”

Frank fiddled with his centurion badge. “I always knew fire could kill me, but since my grandmother’s mansion burned down in Vancouver…it seems a lot more real.”

Leo nodded. He felt sympathy for Frank, but the guy didn’t make it easy when he talked about his family mansion. Sort of like saying, I crashed my Lamborghini, and waiting for people to say, Oh, you poor baby!

Of course Leo didn’t tell him that. “Your grandmother—did she die in that fire? You didn’t say.”

“I—I don’t know. She was sick, and pretty old. She said she would die in her own time, in her own way. But I think she made it out of the fire. I saw this bird flying up from the flames.”

Leo thought about that. “So your whole family has the shape-changing thing?”

“I guess,” Frank said. “My mom did. Grandmother thought that’s what got her killed in Afghanistan, in the war. Mom tried to help some of her buddies, and…I don’t know exactly what happened. There was a firebomb.”

Leo winced with sympathy. “So we both lost our moms to fire.”

He hadn’t been planning on it, but he told Frank the whole story of the night at the workshop when Gaea had appeared to him, and his mother had died.

Frank’s eyes got watery. “I never like it when people tell me, Sorry about your mom.”

“It never feels genuine,” Leo agreed.

“But I’m sorry about your mom.”

“Thanks.”

No sign of Hazel. The American tourists were still milling around the Pantheon. They seemed to be circling closer, like they were trying to sneak up on Raphael’s tomb without it noticing.

“Back at Camp Jupiter,” Frank said, “our cabin Lar, Reticulus, told me I have more power than most demigods, being a son of Mars, plus having the shape-changing ability from my mom’s side. He said that’s why my life is tied to a burning stick. It’s such a huge weakness that it kind of balances things out.”

Leo remembered his conversation with Nemesis the revenge goddess at the Great Salt Lake. She’d said something similar about wanting the scales to balance. Good luck is a sham. True success requires sacrifice.

Her fortune cookie was still in Leo’s tool belt, waiting to be opened. Soon you will face a problem you cannot solve, though I could help you…for a price.

Leo wished he could pluck that memory out of his head and shove it in his tool belt. It was taking up too much space. “We’ve all got weaknesses,” he said. “Me, for instance. I’m tragically funny and good-looking.”

Frank snorted. “You might have weaknesses. But your life doesn’t depend on a piece of firewood.”

“No,” Leo admitted. He started thinking: if Frank’s problem were his problem, how would he solve it? Almost every design flaw could be fixed. “I wonder…”

He looked across the room and faltered. The three American tourists were coming their way; no more circling or sneaking. They were making a straight line for Raphael’s tomb, and all three were glaring at Leo.

“Uh, Frank?” Leo asked. “Has it been ten minutes yet?”