"Ben Franklin's instrument," Dan remembered. "The water on the glass rims thing."

"Yeah, but I have a feeling this is more than a musical score." Amy sat forward. Her eyes were bright, like she knew a secret. "We found the song and downloaded it. Listen."

Nellie handed over her iPod. "Not my kind of music. But whatever."

Dan listened. He felt like he was being filled with helium. The music was so familiar and beautiful it made him want to float across Paris, but it also confused him. Usually he had no trouble remembering things, but he could not recall where he'd heard this music before. "I know this song ..."

"Dad used to play it," Amy said. "In his study, when he was working. He played it all the time."

Dan wanted to remember what Amy was talking about. He wanted to listen to the song over and over until he could see their dad in his study. But Nellie took back the iPod. "Sorry, kiddo. You've still got, like, mud in your ears."

"The notes are a code," Amy said. "The whole piece of music is some kind of message."

"And our parents knew about it," Dan said in amazement. "But what does it mean?"

"I don't know," Amy admitted. "But, Dan, you remember how Mr. McIntyre said the thirty-nine clues are pieces of a puzzle?"

"Yeah."

"I started thinking about that last night, after you decoded that message on the vial.

I started wondering ... why wasn't the first clue like that?"

She brought out the crème paper they'd paid two million dollars for. Dan's scrawled notes filled the back side. On the front side was their first clue:

RESOLUTION:

The fine print to guess,

Seek out Richard S___

Nellie frowned. "That led you to Franklin, right? Wasn't that the answer?"

"Only partly," Amy said. "It's also the first piece of the puzzle. It's a clue to an actual thing.

That clicked for me last night when you mentioned anagrams, Dan."

He shook his head. "I don't get it."

She took out a pen and wrote RESOLUTION. "You asked me why this word was part of the clue. I didn't understand until now. We're supposed to guess the fine print." She passed the paper and pen to Dan. "Solve the anagram."

Dan stared at the letters. Suddenly, he felt like he'd been zapped by a Frankin battery.

The letters rearranged themselves in his mind.

He picked up the pen and wrote: IRON SOLUTE

"I don't believe it," Nellie said. "This whole thing was about iron solute?"

"It's the first piece of the puzzle," Amy said. "It's an ingredient, or a component, or something like that."

"For what?" Dan asked.

Amy pursed her lips. "Iron solute could be used for chemistry, or metalworking, or even printing. There's no way to tell, yet. And we don't know how much we're supposed to use. Every time Franklin mentioned iron solute, he just wrote '1 quantity.'"

"We've got to find out!"

"We will," Amy promised. "And the sheet music..."

She spread her hands over the adagio score.

"It's an ingredient, too," Nellie guessed.

"I think so," Amy said. "That's how you can tell the big clues. They give you an actual ingredient. We just don't know how to read this one yet."

"But how do we find out?" Dan protested.

"The same way we did with Franklin. We find out about the person who wrote it. The composer was -- " Amy stopped abruptly.

Coming down the street was a familiar figure -- a thin balding man in a gray suit, carrying a cloth suitcase. "Mr. McIntyre!" Dan cried.

"Ah, there you are, children!" The old lawyer smiled. "May I?"

Amy quickly folded the first and second clues and put them away. Mr. McIntyre sat with them and ordered a coffee. He insisted on paying for their breakfast, which was okay by Dan, but Mr. McIntyre seemed nervous. His eyes were bloodshot. He kept glancing across the Champs-élysées as if he was afraid he was being watched.

"I heard about last night," he said. "I'm so sorry."

"It's no big deal," Dan said.

"Indeed. I'm sure you'll be able to backtrack. But is it true? Did the Kabras really steal the second clue from under your noses?"

Dan got annoyed all over again. He wanted to brag about the sheet music they'd found and the iron solute thing, but Amy cut in.

"It's true," she said. "We have no idea where to go next."

"Alas." Mr. McIntyre sighed. "I fear you can't go home. Social Services are still on alert.

Your aunt has hired a private detective to find you. And you cannot stay here. Paris is such an expensive city."

His eyes fixed on Amy's necklace. "My dear, I do have friends in the city. I know this would be a desperate measure, but I could possibly arrange a sale for your grandmother's -- "

"No, thank you," Amy said. "We'll get by just fine."

"As you wish." Mr. McIntyre's tone made it clear he didn't believe her. "Well, if there's anything I can do. If you need advice -- "

"Thanks, Mr. McIntyre," Dan said. "But we'll figure it out."

The old lawyer studied them both. "Very good. Very good. I fear there's one more thing I must ask of you."

He reached down for his cloth bag, and Dan noticed the claw marks on his hands.

"Whoa, what happened to you?"

The old man winced. "Yes, well..."

He plopped the bag on the table. Something inside said, "Mrrrp!"

"Saladin!" Amy and Dan cried together. Dan grabbed the bag and unzipped it. The big silver cat slinked out, looking indignant.

"I'm afraid we didn't get along." Mr. McIntyre rubbed his scarred hands. "He was not happy when you left him with me. He and I... well, he made his feelings quite clear that he wanted to be returned to you. It was quite a task getting him through customs, I don't mind telling you, but I really felt I had no choice. I hope you'll forgive me."

Dan couldn't help grinning. He hadn't realized just how much he'd missed the old cat.

Somehow, having him here made up for losing the vial. It even made him feel a little better about losing his parents' photograph. With Saladin around, he felt like his family was complete. For the first time in days, he thought maybe, just maybe, Grace was still looking out for them. "He's got to come with us. He can be our attack cat!"

Saladin stared at him as if to say,

Show me some red snapper, kid, and I'll think about it.

Dan expected Amy to argue, but she was smiling as much as he was. "You're right, Dan. Mr. McIntyre, thank you!"

"Yes, er, of course. Now if you'll excuse me, children. I wish you good hunting!"

He left a fifty-euro bill on the table and hurried out of the café, still looking around like he expected an ambush.

The waiter brought milk in a saucer and some fresh fish for Saladin. Nobody at the café seemed to think there was anything strange about sharing breakfast with an Egyptian Mau.

"You didn't tell Mr. McIntyre about the music," Nellie said. "I thought he was your friend."

"Mr. McIntyre told us to trust no one," Amy said.

"Yeah," Dan said. "And that includes him!"

Nellie crossed her arms. "Does that include me, too, kiddo? What about our agreement?"

Dan was stunned. He'd completely forgotten that Nellie had only promised to come with them on one trip. His heart sank. He'd started taking Nellie for granted. He wasn't sure what they would do without her.

"I... I trust you, Nellie," he said. "I don't want you to leave."

Nellie sipped her coffee. "But you're not going back to Boston. Which means if I go back, I'll get in huge trouble."

Dan hadn't thought of that, either. Amy stared guiltily at her breakfast.

Nellie inserted her earbuds. She watched a couple of college-age guys walking down the road. "This hasn't been a bad job, I guess -- I mean, if I have to work with two annoying kids. Maybe we could make a different deal."

Dan shifted uncomfortably. "A different deal?"

"Someday when you find your treasure," Nellie said, "you can reimburse me. For now, I'll work for free. Because if you kiddos think I'd let you fly around the world and have fun without me, you're crazy."

Amy threw her arms around Nellie's neck.

Dan grinned. "Nellie, you're the best."

"I know that," she said. "C'mon, Amy, you're messing up my street cred."

"Sorry," Amy said, still grinning. She sat down again and brought out the music score.

"Now, as I was saying -- "

"Oh, right, the composer," Dan remembered. Amy pointed at the bottom of the paper.

"Look." In the right-hand corner below the last stanza, Dan made out three scrawled letters in faded black ink:

W. A. M.

"Wam," Dan said. "Wasn't that a band?"

"No, dummy! Those are initials. I told you some famous people made music for Benjamin Franklin's armonica. This guy was one of them. Toward the end of Franklin's life, he must've met this composer. I think they were both Cahills. They must've shared secrets. Anyway, I looked it up. This was the composer's last piece of chamber music. Its official name is KV 617."

"Catchy title," Nellie muttered.

"The thing is," Amy said, "there are lots of copies of this adagio. And there's still the version carved in stone on that pedestal. The other teams will figure out the clue eventually. We have to hurry and get to Vienna."

"Whoa, hold on," Dan said. "Vienna, Austria? Why there?"

Amy's eyes twinkled with excitement. "Because that's where Wolfgang Amadeus Mozart lived. And that's where we'll find the next clue."

CHAPTER 20

William McIntyre made his appointment just in time.

He stepped out onto the observation deck of the Eiffel Tower. The day after a heavy rain, the air was clean and fresh. Paris glistened below as if all its dark secrets had been washed away.

"They didn't trust you," the man in black said.

"No," William admitted.

His colleague smiled. "They learn quickly."

William McIntyre kept his annoyance in check. "Things could have gone worse."

"They could have gone much better. We will have to watch them more closely, don't you think?"

"Already taken care of." William McIntyre took out his cell phone. He showed his colleague the screen -- the last number he had dialed in Vienna, Austria.

The man in black made a low whistle. "Are you sure that's wise?"

"No," William admitted. "But necessary. Next time, there can be no mistakes."

"No mistakes," the man in black agreed. And together, they watched the city of Paris spread out below them, ten million people completely unaware that the fate of the world hung in the balance.