"I'm getting a headache," Sinead Starling said.

"How you proceed is entirely up to you," Mr. McIntyre said. "But remember: You all seek the same end, and only one team will succeed. Speed is of the essence."

Irina Spasky folded her clue, stuck in it her purse, and walked out the door.

Alistair Oh frowned. "It seems Cousin Irina has an idea."

The Starling triplets put their heads together. Then, as if they'd gotten a collective brain flash, they stood up so fast they knocked over their chairs and ran outside.

Jonah Wizard's dad pulled him into the corner. They had a heated discussion and his dad typed some stuff into his BlackBerry.

"Gotta jet," Jonah said. "Later, losers." And off they went.

That made three teams already out the door, and Dan still had no idea what the clue meant.

"Well." Ian Kabra stretched lazily, like he had all the time in the world. "Are you ready, dear sister?"

"To make fools of our American cousins?" Natalie smiled. "Anytime."

Dan tried to trip them as they walked past, but they nimbly stepped over his leg and kept going.

"All right!" Mr. Holt announced. "Team, form up!"

The Holt clan shot to their feet. Their buff little pit bull, Arnold, barked and leaped around them like he was trying to bite their noses.

"Where we going, Dad?" Hamilton asked.

"I don't know. But everybody else is leaving! Follow them!"

They marched double-time out of the Great Hall, which left only Amy, Dan, Alistair Oh, and William McIntyre.

"Dear me," Alistair sighed. With his black suit and silk cravat, he reminded Dan of a butler. A butler with a secret. His eyes seemed to be smiling, even when he wasn't. "I think I'll have a stroll around the grounds and think about this."

Dan was thankful to see him leave. Alistair seemed like the nicest of their competition, but he was still competition.

Dan stared at the clue again, more frustrated than ever. "Resolution. Fine print.

Richard S -- . I don't get it."

"I can offer you no help with the clue." Mr. McIntyre managed a faint smile. "But your grandmother would be pleased you accepted the challenge."

Amy shook her head. "We don't stand a chance, do we? The Kabras and the Starlings are rich. Jonah Wizard's famous. The Holts are like steroid monsters. Alistair and Irina seem so -- I don't know -- worldly.

And Dan and I -- "

"Have other talents," Mr. McIntyre finished. "As I'm sure you'll find out."

Dan reread the clue. He thought about baseball cards, and letters, and autographs.

"We're supposed to find this guy Richard," he decided. "But why is his last name just S___?"

Amy's eyes widened. "Wait a minute. I remember reading that back in the 1700s, people used to do that. They would use only one letter if they wanted to disguise their names."

"Huh," Dan said. "So, like, I could say A -- has a face like a baboon butt, and you wouldn't know who I'm talking about?"

Amy boxed him on the ear.

"Ow!"

"Children," Mr. McIntyre interrupted. "You will have enough enemies without fighting each other. Besides" -- he checked his gold pocket watch -- "we don't have much time, and there is something I must tell you, something your grandmother wanted you to know."

"An inside tip?" Dan asked hopefully.

"A warning, young master Dan. You see, all Cahills -- if they know themselves to be Cahills -- belong to one of four major branches."

Amy stood up straight. "I remember this! Grace told me once."

Dan frowned. "When did she tell you that?"

"In the library one afternoon. We were talking."

"She didn't tell me!"

"Maybe you weren't listening! There are four branches. The Ekaterina, the Janus, the ... uh, Tomas, and the Lucian."

"Which are we?" Dan asked.

"I don't know." Amy looked at Mr. McIntyre for help. "She just mentioned the names. She wouldn't tell me what we are."

"I'm afraid I can't help you there," Mr. McIntyre said, but Dan could tell from his tone that he was keeping something back. "However, children, there is another ... ah, interested party you should know about. Not one of the four Cahill branches, but a group that may make your quest more difficult."

"Ninjas?" Dan asked excitedly.

"Nothing quite that safe," Mr. McIntyre said. "I can tell you very little about them. I confess I know only the name and a few unsettling stories. But you must beware of them. This was your grandmother's last warning, which she made me promise to tell you if you accepted the challenge:

Beware the Madrigals."

A chill went down Dan's back. He wasn't sure why. The name Madrigals just sounded evil. "But, Mr. McIntyre, who -- "

"My boy," the old man said, "I can tell you no more. I've stretched the rules of the competition saying as much as I have. Just promise me you will trust no one. Please. For your own safety."

"But we don't even know where to start!" Amy protested. "Everyone else just rushed off like they knew what to do. We need answers!"

Mr. McIntyre stood. He closed his leather folder. "I must get back to my office. But, my dear, perhaps your way of finding out is not the same as the other teams'. What do you normally do when you need answers?"

"I read a book." Amy gasped. "The library! Grace's library!"

She raced out of the Great Hall. Usually, Dan did not run with excitement when his sister suggested visiting a library. This time, he did.

The library was next to Grace's bedroom -- a big sunken parlor lined with bookshelves.

Dan thought it was creepy being back here with just Amy, especially since Grace had died next door in her big four-poster bed. He expected the rooms to be all draped in black, with sheets over the furniture like you saw in movies, but the library was bright and airy and cheerful, just like it had always been.

That didn't seem right to Dan. With Grace gone, the mansion should be dark and dreary -- kind of the way he felt. He stared at the leather chair by the window and remembered one time he'd been sitting there, playing with a cool stone dagger he'd busted out of a locked display case. Grace had come up so quietly he didn't notice her until she was standing right over him. Instead of getting mad, she'd knelt next to him.

That dagger is from Tenochtitlán, she'd said.

Aztec warriors used to carry these for ritual sacrifice. They would cut off the parts of their enemies that they believed held their fighting spirit.

She'd showed him how sharp the blade was, and then she left him alone. She hadn't told him to be careful. She hadn't gotten angry because he'd busted into her cabinet.

She'd acted like his curiosity was totally normal -- even admirable.

No adult had ever understood Dan that well. Thinking about it now, Dan felt like somebody had cut away part of his spirit.

Amy started searching the library books. Dan tried to help, but he had no idea what he was looking for and quickly became bored. He spun the old globe with brown seas and weird-colored continents, wondering if it would make a good bowling ball. Then he noticed something he'd never seen before under the Pacific Ocean -- a signature.

Grace Cahill, 1964.

"Why did Grace autograph the world?" he asked. Amy glanced over. "She was a cartographer. A map-maker and an explorer. She made that globe herself."

"How did you know that?"

Amy rolled her eyes. "Because I listened to her stories."

"Huh." That idea had never occurred to Dan. "So where'd she explore?"

A man's voice said, "Everywhere."

Alistair Oh was leaning on his cane in the doorway, smiling at them. "Your grandmother explored every continent, Dan. By the time she was twenty-five, she could speak six languages fluently, handle a spear or boomerang or rifle with equal skill, and navigate almost every major city in the world. She knew my hometown of Seoul better than I did. Then, for reasons unknown, she came back to Massachusetts to settle down. A woman of mystery -- that was Grace."

Dan wanted to hear more about Grace's boomerang skills. That sounded sweet! But Amy stepped away from the bookcase. Her face was bright red. "A-Alistair. Uh ... what do you want?"

"Oh, don't let me stop you. I won't interfere."

"Um, but... there's nothing here," Amy mumbled. "I was hoping for ... I don't know.

Something I hadn't seen before, but I've read most of these. There really aren't that many books. And there's nothing about Richards-."

"My dear children, may I suggest something? We need an alliance."

Dan was immediately suspicious. "Why would you want an alliance with a couple of kids?"

The old man chuckled. "You have intelligence and youth, and a fresh way of looking at things. I, on the other hand, have resources and age. I may not be one of the most famous Cahills, but I did change the world in my own small way. You know my fortune comes from inventions, eh? Did you know I invented the microwavable burrito?"

"Wow," Dan said. "Earth-shattering."

"There's no need to thank me. The point is I have resources at my disposal. And you can't travel around the world on your own, you know. You'll need an adult chaperone."

Around the world?

Dan hadn't thought about that. He hadn't even been allowed to go on the fourth grade field trip to New York last spring because he'd put Mentos in his Spanish teacher's Diet Coke. The idea that this clue hunt might take them anywhere in the world made him feel a little lightheaded.

"But -- but we can't help each other," Amy said. "Each team is separate."

Alistair spread his hands. "We can't both win.

But this challenge may take weeks, perhaps months. Until the end, surely we can collaborate? We are family, after all."

"So give us some help," Dan decided. "There's nothing here about Richard S___ .

Where do we look?"

Alistair tapped his cane on the floor. "Grace was a secretive woman. But she loved books. She loved them very much. And you're right, Amy. It does seem strange there are so few of them here."

"You think she had more books?" Amy cupped her hand over her mouth. "A ... a secret library?"

Alistair shrugged. "It's a large house. We could split up and search."

But then Dan noticed something -- one of those random little details that often caught his eye. On the wall, at the very top of the bookshelf, was a plaster crest just like above the front door of the mansion, a fancy C surrounded by four smaller coats of arms -- a dragon, a bear, a wolf, and a pair of snakes wrapped around a sword. He must've seen this before a million times, but he'd never noticed that the smaller crests each had a letter carved in the middle -- E, T, J, L.

"Get me a ladder," he said.

"What?" Alistair asked.

"Never mind," Dan decided. He began to climb the shelf, knocking down books and knickknacks.

"Dan, get down!" Amy protested. "You're going to fall and break your arm again! "

Dan had reached the crest, and he saw what to do. The letters were smudged darker than the rest of the stone, like they'd been touched many times.