"It was Irina Spasky’s fault!" Dan said. "She tricked us into going there. The whole thing was a setup."

"And we can’t even pay you," Amy added miserably. "We don’t have enough money for the flight home. I’m … I’m really sorry, Nellie."

Nellie stood very still. Her glitter eye shadow was red today, which made her eyes look even angrier. Her arms were crossed over her T-shirt, which showed a picture of a screaming punk rocker. All in all, she looked pretty scary. Then she grabbed Amy and Dan and hugged them fiercely.

She knelt down so she was looking them in the eyes. "I’ve got some credit left on my MasterCard. We’ll be fine."

Dan was confused. "But … you’re not going to kill us?"

"I’m going to help you, stupid." Nellie shook his shoulders gently. "Nobody messes with my babysitees."

"Au pairees," Dan corrected.

"Whatever! Now get some sleep. Tomorrow we’re going to slap some people senseless."

Maison des Gordons did not mean the house of gardens. Apparently, gardons meant roaches. Dan found this out because Nellie told him, and because he heard scuttling sounds along the floor all night long. He wished Saladin were there. The cat would’ve had a great time playing jungle stalker.

In the morning, everybody looked bleary-eyed, but they showered and changed clothes. Nellie came back from the corner café with coffee for herself, hot chocolate for Dan and Amy, and pain au chocolat for al of them. Dan figured any country that ate chocolate for breakfast couldn’t be all bad.

"So," Dan said, "can I get some more grenades today?"

"No!" Amy said. "Dan, you’re lucky it was only concussive. You could’ve wiped out the whole Holt family."

"And that would’ve been bad because … ?"

"Okay, knock it off," Nellie said. "The important thing is you guys are safe."

Amy picked at her croissant. She looked pale this morning. Her hair was a tangled mess. "Dan … I’m sorry about last night. I — I panicked. I almost got us killed."

Dan had pretty much forgotten that part. He’d been annoyed with her at the time, but it was hard to stay mad when Amy looked so miserable and apologized.

Plus she’d done that cool thing with the battery, which had kind of made up for her freaking out.

"Don’t worry about it," he said.

"But if it happens again — "

"Hey, if we let Irina lure us into a trap again, we’re stupider than the Holts."

Amy didn’t look very comforted. "What I don’t understand is the man in black. Why was he there last night? And if the Holts started the fire at the mansion and set up the museum explosion — "

"Then what was the man in black doing in both places?" Dan finished. "And why did Irina have a photo of him?"

He waited for Amy to come up with one of her "oh-I-did-a-book-report-on-that-last-year" answers, but she just kept frowning at her breakfast.

"Maybe you guys should concentrate on where we go next," Nellie advised.

Amy took a deep breath. "I think I know where to go. Dan, can I use your laptop?"

He stared at her, because Amy didn’t like computers. But finally he brought it over and Amy started searching the Internet.

In no time, she grimaced and turned the screen for them to see. The picture showed a pile of bones in a dark stone room.

"I’ve suspected for a while," Amy said, "but I was hoping I was wrong because it’s risky. The Maze of Bones. That’s what Mom’s note said in Poor Richard’s Almanack. We have to explore the Catacombs."

"Is that where they keep the cats?" Dan asked.

It seemed like a perfectly reasonable question to him, but Amy gave him a "you’re-such-a-dummy" look.

"The Catacombs are an underground maze," she said. "I told you Paris is riddled with caves and tunnels, right? Al the limestone they used to build the city, ever since the Roman days, they dug from underground, and it left a whole network of empty spaces.

Some are just pits, like the one we fell in last night."

"And some are networks of tunnels," Nellie said. "Yeah, I remember hearing about this. And they’re filled with bones, right?"

"I want a room decorated with bones!" Dan said. "Where’d they come from?"

"Cemeteries," Amy said. "Back in the 1700s, the cemeteries were getting overcrowded, so they decided to dig up tons of old bodies — all their bones — and move them into the Catacombs. The thing is … look at the dates. See when they started moving bones into the Catacombs?"

Dan squinted at the screen. He didn’t see what she was talking about. "Is it my birthday?"

"No, doofus. Look. 1785. They didn’t officially declare it open until the next year, but they started planning the project, and moving the bones, in 1785. Which was also the last year Benjamin Franklin was in Paris."

"Whoa. You mean — "

"He hid something down there." It got so quiet Dan could hear roaches scuttling in the closet.

"So," Nellie said, "we have to go underground, into a maze filled with bones, and find … whatever it is."

Amy nodded. "Except the Catacombs are huge. We don’t know where to look. The only thing I can think — there’s one public entrance. It says here it’s across from the Denfert-Rochereau Métro station, in the 14th arrondissement."

"But if that’s the only public entrance," Dan said, "then the other teams might head there, too. Everybody’s been stealing that almanac from each other. They’ll figure out the Maze of Bones thing eventually, if they haven’t already."

"Good enough for me." Nellie brushed the chocolate and bread crumbs off her shirt.

"Let’s go meet your family."

Dan’s backpack was a lot lighter today, but before they left he made sure the photo of his parents was still safe in the side pocket. His mom and dad were right where he’d left them: in their plastic photo album sheet, smiling from the top of their mountain like they hadn’t minded sharing space with a Franklin battery and a grenade at all.

He wondered if they’d be proud of him for getting out of that pit last night, or if they’d be all protective like Amy: You almost got yourself killed, blah, blah, blah. He decided they would’ve been cooler than that. They’d probably had tons of dangerous adventures. Maybe their house had an arsenal, too, before it burned down.

"Dan!" Amy called. "Get out of the bathroom and let’s go!"

"Coming!" he shouted. He looked at his parents one more time. "Thanks for the note about the Maze of Bones, Mom. I won’t let you down!"

He slipped the photo back into his pack and went to join Amy and Nellie.

They weren’t out of the Denfert-Rochereau Métro station two minutes before they spotted Uncle Alistair. He was kind of hard to miss in his cherry-red suit and canary-yellow ascot, his diamond-tipped cane swinging in one hand. The old man sauntered toward them, smiling with his arms out. As he got closer, Dan noticed he had a black eye. "My dear children!"

Nellie whopped him upside the head with her backpack.

"Ow!" Uncle Alistair curled over, cupping his hand over his good eye. "Nellie!" Amy said.

"Sorry," Nellie muttered. "I thought he was one of the bad guys."

"He is," Dan agreed.

"No, no." Alistair tried to smile, but all he could do was wince and blink. Dan figured his other eye was going to be black now thanks to that pop. Nellie’s backpack was not light.

"Children, please, you must believe me, I am not your enemy!"

"You stole the book from us," Dan said, "and left us for dead!"

"Children, I admit it. I thought you were lost in the fire. I barely made it out myself.

Fortunately, I found a latch that opened the door. I called for you, but you must have discovered another way out. I had the almanac, yes. I couldn’t leave it behind. I admit I panicked when I got outside. I feared our enemies were still about, or that I would be blamed for the terrible fire. So I fled. Forgive me."

Amy’s scowl softened, but Dan didn’t believe this guy at all.

"He’s lying!" Dan said. "Trust no one,’ remember?"

"Should I hit him again?" Nellie asked.

Uncle Alistair flinched. "Please, listen. The Catacombs are right there." He pointed across the street to a simple building with a black facade. White letters above the door read Entrée des Catacombes.

The street around it looked like a normal neighborhood — townhouses, apartments, pedestrians on their way to work. It was hard to believe a maze of dead people lay right underneath.

"I must speak with you before you go in," Alistair insisted. "All I ask is ten minutes. You are in grave danger."

"Grave danger," Dan grumbled. "That supposed to be a joke?"

"Dan …" Amy put her hand on his arm. "Maybe we should listen to him. Ten minutes. What do we have to lose?"

Dan could think of a lot of things, but Alistair smiled. "Thank you, my dear. There is a café just here. Shall we?"

Alistair was buying, so Dan ordered an early lunch — a turkey-and-cheese sandwich with chips and a large Coke, which for some weird reason was delivered in a glass with no ice. Nellie spoke with the waiter in French for a long time and ordered some exotic gourmet thing. The waiter looked impressed with her choice, but when it came Dan couldn’t tell what it was. It looked like gobs of Silly Putty in garlic butter.

In a sad voice, Alistair explained how the Holts had ambushed him outside de Gaulle Airport and taken the

Poor Richard’s Almanack.

"The barbarians hit me in the face and cracked one of my ribs. I really am getting too old for this sort of thing." He touched his bruised eyes.

"But … why is everyone trying to kill each other over that book?" Amy asked. "Aren’t there other ways to find the clue? Like the invisible message we found in Philadelphia — "

"Amy!" Dan said. "Keep secrets much?"

"It’s all right, my boy," Alistair said. "You’re correct, of course, Amy. There are many possible paths toward the next clue. For instance, I found a message encoded in a famous portrait by — well, here, see for yourself."

Uncle Alistair reached into his coat and pulled out a paper. He unfolded a color print of a painting. It showed Benjamin Franklin as an old man in a red flowing robe, sitting in a thunderstorm, which seemed kind of dumb. A bunch of baby angels hovered around him — two at his feet, working on batteries, and three more right behind him, holding up a kite with a key on the string. Lightning zapped from the key into Ben’s upraised hand. Ben didn’t look upset by this. His long gray hair was wild and frizzed out, so maybe he was used to getting shocked.

"No way did it happen like that," Dan said. "With the angels and all."

"No, Dan," Alistair agreed. "It’s symbolic. The painter, Benjamin West, meant to show Franklin as a hero for drawing lightning out of the sky. But there is more symbolism than I realized — signs hidden so deep only a Cahill could discover them. Look at Franklin’s knee."

Dan didn’t see anything except a knee, but Amy gasped. "That shape in the fabric!"

Dan squinted, and he saw what she meant. Part of Franklin’s knee was painted in a lighter shade of red, but it wasn’t just a random blotch. It was a silhouette he’d seen many times before.