The Maze of Bones (The 39 Clues #1)(20)

"That's impossible!" Amy said. "Nobody knew we'd be here."

But as she said it, a chill went down her back. They'd booked the train tickets and the rental car online last night from their hotel, using Nellie's name. Was it possible somebody had tracked them down so fast?

"What does the envelope say?" Dan asked.

"'For A. & D. Cahill,'" Nellie read. '"From W. McIntyre.'"

"Mr. McIntyre!" Dan grabbed the package.

"Wait!" Amy yelled. "It could be a trap."

Dan rolled his eyes. "C'mon. It's from -- "

"It could be from anybody," Amy insisted. "It could blow up or something."

"Okay, whoa," Nellie said. "Why would somebody send a couple of kids a bomb? And who is this McIntyre dude?"

Dan grinned. "I say we let Nellie open it."

"Um, no!" Nellie said.

"You're the au pair! Aren't you supposed to defuse explosives for us and stuff?"

"I'm driving you, kiddo. That's enough!"

Amy sighed and snatched the package. She stepped into the parking lot, turned the flap of the envelope away from Nellie and Dan, and carefully peeled it open.

Nothing happened. Inside was a metal cylinder like a flashlight, except the light was a strip of purple glass running down one side. A note was attached in sloppy handwriting, like the writer had been in a hurry:

Meet me at Independence Hall this evening at eight, but only if you find the information

-- WM

(P.S. Thank you for calling the ambulance.)

"Find what information?" Dan asked, reading over her shoulder.

"The next clue, I guess."

"What clue?" Nellie demanded.

"Nothing," Dan and Amy said.

Nellie blew a tuft of black and blond hair out of her eyes. "Whatever. Stay right here.

I'll bring the car around."

She left them standing with the bags and Saladin in his new cat carrier. Saladin hadn't been too pleased with the cat carrier -- anymore than Nellie had been with the fresh red snapper they'd bought to keep him happy -- but Amy hadn't had the heart to leave him behind.

"Mrrp?"

Saladin asked.

Amy reached down and scratched his head through the bars. "Dan, maybe we shouldn't make that rendezvous. Mr. McIntyre told us not to trust anyone."

"But the note is from him!

""It could be a trick."

"That makes it even better! We've got to go!"

Amy twisted her hair. She hated it when Dan didn't take her seriously. And this could be dangerous.

"If we go, it says we have to find information first."

"But you know where to look, right? You're smart and stuff."

Smart and stuff.

Like that's all they needed to track down a clue in a huge city. Before they'd left Boston, she'd splurged and bought some books about Franklin and Philadelphia from her friends at the used bookshop. She'd spent the whole train trip reading, but still....

"I've got a few ideas," she admitted. "But I don't know where we're going in the long term. I mean -- have you thought about what this ultimate treasure could be?"

"Something cool."

"Oh, that's real helpful. I mean, what could make somebody the most powerful Cahill in history? And why thirty-nine clues?"

Dan shrugged. "Thirty-nine is a sweet number. It's thirteen times three. It's also the sum of five prime numbers in a row -- 3, 5, 7, 11, 13.

And if you add the first three powers of three, 3 (raised to the first power) plus 3 (raised to the second power) plus 3 (raised to the third power), you get thirty-nine."

Amy stared at him. "How did you know that?"

"What do you mean? It's obvious."

Amy shook her head in dismay. Dan acted like a doofus most of the time. Then he'd pull something like that -- adding prime numbers or powers of three that she'd never thought about. Their dad had been a mathematics professor, and Dan apparently had inherited all of his number sense. Amy had enough trouble remembering phone numbers.

She held up the weird metal cylinder Mr. McIntyre had sent them. She switched it on and the light glowed purple.

"What is that thing?" Dan asked.

"I don't know," Amy said. "But I have a feeling we'd better figure it out before eight o'clock."

Amy hated cars almost as much as she hated crowds. She promised herself that when she got older she'd live somewhere where she never had to drive. Part of that was because she'd been in the car with Nellie before.

Nellie had rented a Toyota hybrid. She said it was more environmental, which was fine with Amy, but it cost two hundred and fifty-eight dollars a day, and the way Nellie raced around corners and gunned the gas wasn't exactly "green."

They were on Interstate 95, heading into downtown, when Amy happened to look behind them. She wasn't sure why -- a prickling sensation on her neck like she was being watched. In fact, she was.

"We're being followed," she announced.

"What?" Dan said.

"Five cars back," Amy said. "Gray Mercedes. It's the Starlings."

"A Starbucks?" Nellie said excitedly. "Where?"