Franklin had written lots of letters to his friends and family while living in Europe.

Follow Franklin. A crazy idea started to form in her head.

Amy looked at the librarian. "You said his letters were important to him. Is there anyplace else that keeps Franklin's letters on display?"

The librarian smiled. "Funny you should ask. Some of his most famous handwritten documents are showing this month at the Franklin Institute down on -- "

"The science museum?" Amy shot to her feet. "On 20th Street?"

"Yes." The librarian looked startled. "But how did you -- "

"Thanks!" Amy rushed out of the room with Dan right behind her.

It was a quick drive to the Franklin Institute. Nellie wasn't too thrilled to sit in the car with the cat again, but Dan and Amy convinced her they wouldn't be long. They ran inside and found a twenty-foot-tall white marble statue of Benjamin Franklin gazing down at them from a giant chair in the entry chamber.

"Holy almanacs," Dan said. "That's a big Ben."

Amy nodded. "At the end of his life, he was so heavy he had to be hauled around in a sedan chair carried by four big convicts."

"Sweet," Dan said. "I want a sedan chair."

"You weigh ninety pounds."

"RESOLUTION: Start eating more ice cream."

"Just come on!"

The museum was huge. They walked past the memorial and through the ticket area, then followed the map into the Franklin Gallery. It was already late in the afternoon and the place was pretty much deserted.

"Check this out!" Dan picked up a mechanical arm and grabbed Amy's wrist with it.

"Stop that!" she said. "Franklin made that for getting things off high shelves, not annoying your sister."

"I bet if he had a sister -- "

"He did have a sister! Dan, we need to find his letters. Stop messing around."

They kept walking .They found a display of Franklin's lightning rods, a bunch of bifocals, and one of his batteries for generating electricity -- a wooden crate full of glass jars, all wired together.

"That thing is huge," Dan said. "What is that, like, a double Z battery? And whoa, what is that?"

He ran over to another display. Inside was a mahogany box holding a row of closely fitted glass saucers, like a stack of cereal bowls.

"It's an armonica," Amy said, reading the description. "It makes music by rubbing water on the rims of the glasses."

"Awesome. Franklin invented that?"

"Yeah. Says here it was really popular for a while. Lots of famous composers wrote music for ..."

Amy froze. A tall gray-haired man had just crossed the hallway in the next gallery, heading toward the information desk. And he was wearing a black suit.

"What?" Dan asked.

"Man in black," Amy murmured. "Run!"

She grabbed her brother's hand and they fled deeper into the gallery. They didn't stop until they were two rooms away, hiding behind a large glass sphere that showed the solar system.

"What's he doing here?" Amy fretted.

"Duh," Dan said. "The fire didn't work, so he's here to get us! We can't go out the main exit. He'll be waiting to jump us as soon as we try."

Amy looked around nervously for another way out. Then she noticed what was on the wall right next to them. Documents. Cases full of documents -- all yellowing parchment, written in spidery handwriting.

"Franklin's letters!" she said. "Quick, the black light reader!"

Dan fumbled in his backpack and brought out the light. They held it up to the first letter and shone it through the glass. The document seemed to be some kind of request for supplies. It started:

Sir, I wrote to you lately via New York, which I hope may come to hand. I have only time now to desire you to send me the following items, viz.

1 Doz. Cole's

Eng. Dictionaries

3 Doz. Mathers Young Man's Compan'n

1 Qty. Iron Solute

2 Quarter Waggoners for

America

Purple light passed over the paper, but nothing happened.

"Next!" Amy said. She was sure the man in black was going to burst in on them any second.

"Whoa!" Dan said.

Amy gripped his arm. "You found it?"

"No, but look! This whole essay -- 'To the Royal Academy.' He wrote a whole essay on farts!" Dan grinned with delight. "He's proposing a scientific study of different fart smells. You're right, Amy. This guy was a genius!"

"Dan, you're such a dweeb! Keep searching!"

They scanned four more documents written by Franklin. Nothing showed up. Then, on the fifth one, Dan said, "Here!"

Thankfully, it wasn't another fart essay. The letter was something Franklin had written in Paris in 1785 to someone named Jay. Amy didn't know what it was about. She didn't have time to read it. But glowing yellow in the black light beam were lines between the lines -- a secret message in the handwriting of Benjamin Franklin:

Soon must I leave

This place of wonder

But I leave behind

What hath driven my clan asunder.

Below, drawn by hand, was a crest with two snakes coiled around a sword.

Amy gasped. "That's one of the crests from Grace's library -- the one with the L. Franklin must've been a Lucian!"

"So this is the second clue?" Dan asked. "Or a clue to the clue?"

A camera clicked. "Either way," a girl's voice said. "Nice job."

Amy turned and found herself surrounded by the Starlings. They wore identical preppy clothes as usual -- 12 khakis, button-downs, and loafers. Sinead's auburn hair was tied back in a ponytail. Her brothers, Ted and Ned, stood on either side of her, smiling in an unfriendly way. Sinead was holding her cell phone, which she'd obviously just used to take a photo of their clue.

"You lost us pretty well on the highway," Sinead admitted. "Fortunately, there were only so many Franklin sites you could've been heading to. Thanks for the clue."

She snatched the black light reader away from Dan. "Now, listen close. You brats are going to stay in the museum for half an hour. Give us a head start or we'll be forced to tie you up.

If you leave early, I promise Ted and Ned will find out about it. And they won't be happy."

Her two brothers grinned evily. Sinead turned to leave, but Amy blurted out,

"W-w-wait!"

Sinead raised an eyebrow.

"Th-there's a man ..." Amy tried to say more, but the Starlings were all glaring at her.

She felt like she'd been submerged in ice water.

"What man?" Sinead asked.

"He's been watching us!" Dan said. "Following us! It isn't safe to go out the main entrance."

Sinead smiled. "You're concerned for our safety? That's very cute, Dan, but the thing is" -- Sinead leaned in and poked him in the stomach with every word -- "I DON'T BELIEVE YOU."

Sinead and her brothers laughed, then turned and jogged toward the main exit.

Before Amy could even think what to do, a low horrible hum shook the floor. And then:

BOOOM!

Glass display cases shattered. The whole building shuddered. Amy was thrown against Dan and they crumpled to the floor.

When she sat up, her vision was fuzzy. She wasn't sure how long she stayed there, dazed. She staggered to her feet and tugged on Dan's arm.

"Get up!" she said, but she couldn't hear her own voice.

"What?" he mouthed.

She hauled him to his feet. Together they ran toward the exit. Smoke and dust filled the air. Emergency lights flashed from the fire alarms. A pile of rubble blocked the exit from the Franklin Gallery, as if part of the ceiling had collapsed. On the floor near Amy's feet lay the shattered black light reader and Sinead's cell phone.

And there was no sign of the Starlings at all.

CHAPTER 9

Dan decided that explosions were cool, but not if you were in one.

The whole way to Independence Hall, Amy cradled Saladin's cat carrier like it was her life preserver. Nellie yelled at them for being so reckless. Dan's hearing was so messed up she sounded like she was talking from the bottom of a fish tank.

"I can't believe this!" Nellie said. "A real bomb? I thought you were joking!"

Amy wiped her eyes. "The Starlings ... they just -- "

"Maybe they're okay," Dan said, but it sounded lame even to him. They hadn't stuck around for the police to arrive. They'd been so freaked out they'd simply fled, so Dan had no idea what had happened to the triplets. He didn't figure it was a good sign that they'd found Sinead's phone next to a whole section of collapsed roof.

Nellie yanked the wheel and they turned onto Sixth Street. "You guys, this is serious.

Somebody tried to kill you. I can't babysit you if -- "

"Au pair us," Dan corrected, " -- whatever!"

She pulled the car in front of Independence Hall. The sun was going down, and in the evening light, the place looked exactly like it did in school videos -- a two-story brick building with a big white clock tower, surrounded by trees and flower beds. A statue of some Revolutionary dude stood out front. The hall didn't look all that impressive compared to the huge modern buildings around it, but back in the day, Dan guessed it was probably the biggest place in town. He could imagine Franklin and all his friends with powdered wigs and three-cornered hats gathering on the steps to talk about the Declaration of Independence, or the Constitution, or maybe Ben's latest proposal for studying farts. The whole scene made Dan think of American history tests, which were almost as scary as exploding museums.

"Look, guys," Nellie said. "The deal's off. Whatever you've gotten yourselves into -- this is way too dangerous for a couple of kids. I'm going to take you back to your aunt."

"No!" Dan said. "Nellie, you can't. She'll-"

He stopped himself, but Nellie's blue-glitter-shaded eyes narrowed. "She'll what?"

Dan glanced at Amy, hoping for help, but she was still in shock, just staring out the window.

"Nothing," Dan said. "Nellie, this is important. Please. Just wait for us."

Nellie fumed. "I've got, like, six more songs on my playlist, okay? If you're not back in the car when the last song is over, and ready to explain things to me honestly, I am so calling Beatrice."

"You got it!" Dan promised. He tried to push Amy out of the car, but she must've still been in shock, because she held on to Saladin's cat carrier.

"What are you doing?" Dan asked. "Leave him here."

"No." Amy fumbled to cover the carrier with a blanket. "We need to take him."

Dan didn't know why, but he decided not to argue. They hurried along the sidewalk.

They were halfway up the steps of Independence Hall when Dan realized the place was closed for the night. "How do we get in?"

"Children!" a voice called. "Over here!"

William McIntyre was leaning against the building, half hidden behind a rosebush. Amy ran over and gave the old lawyer a hug, which seemed to embarrass him. He had a bandage on his left hand and a cut below his right eye, but other than that he looked pretty good for a guy who'd just gotten out of the hospital.

"I'm glad you're safe," he said. "I heard about the Franklin Institute on the news. I assume you were there?"