Darrell cleared his throat. "Wade's odd behavior means he's worried. Which, I know, is not breaking news, but he found something bizarro on your computer . . ."

Wade pointed at the computer screen. "Dad, I'm sorry, but it was an accident that I saw the screen at all. I know I shouldn't have read the email, but I saw it, and . . . what's going on? It's from Uncle Henry, but it looks like code."

Dr. Kaplan paused for a long moment. His smile faded away. He leaned over Wade and tapped the keyboard. The email printed out on a nearby printer. Then he deleted the message and shut the computer off.

"Not here. Not now."

Chapter Four.

"Can you at least tell us why Uncle Henry's writing to you in code?" Wade asked when they got into the car. "Is he in trouble? Or in danger? Dad, are we in danger?"

"You worry too much," said Dr. Kaplan, unconvincingly.

"Is Uncle Henry a spy?" asked Darrell. "Because if he's a spy, that's huge. A spy in the family would actually be terrific and awesomely cool. As you probably already know, I would make a perfect spy-"

"Boys, please," Dr. Kaplan said, weaving through campus traffic and onto the streets. "I'm sure Uncle Henry is just fine, and I'm almost positive it's some kind of joke message. In any case, it won't make sense to you-or even to me-until we get home. There are a couple pieces of the puzzle I need to figure it out. Until then . . ."

Puzzle? Wade didn't know what to say. He sat quietly looking out the window for the next twenty minutes as they drove from campus into the hills west of Austin.

Darrell did not sit quietly. "I think I have it. Uncle Henry is a professor in Germany, but he's secretly doing spy stuff. He's a master cryptographer, and he's trying to recruit you to be a spy too. Dad, if you can't do it, I'll do it. Sure. I know professors make a good cover. They pretend to sit in their offices all sleepy over their books and stuff while secretly they're running all kinds of spy missions. But middle school kids are even better. No one would ever suspect us. Wade, you could be a spy, too. Of course, you'd do the desk stuff while I go around the world with my band as a cover. Not that the Simpletones would be a cover band. We'd play all original stuff. They call that being in the field. I'd be a field agent. Agent being the technical term for 'spy' . . ."

Darrell hadn't stopped talking, but as he was often forced to do when his stepbrother thrashed on guitar, Wade had to tune him out to be able to think.

Ever since Uncle Henry had given him the antique celestial map on his seventh birthday, Wade had been a fanatic about star maps and charts and the courses and routes of celestial bodies. He'd stayed up every night for weeks studying the map by moonlight and flashlight. Of course, he learned most things from his father, a brilliant astronomer, but it was probably Uncle Henry's star map that stole his deeper imagination. The chart was old and strange and mysterious, and in his mind Wade associated all those qualities with the stars themselves. Between his father and Uncle Henry, Wade learned to love the night sky more than anything.

When they finally turned into the driveway of a sprawling home overlooking a shallow valley, Darrell practically exploded in the backseat. "Uncle Henry is a spy! Someone's casing our house!"

As Dr. Kaplan slowed the car, a shape darted along the side garden and disappeared under the roof that hung over the front door.

Wade stiffened. "Dad, tear out of here-"

"Yoo-hoo!"

A girl in shorts and a stylishly slashed T-shirt strolled out from under the overhang to the car, wheeling an orange suitcase behind her.

It was Lily Kaplan, Wade's first cousin, his father's niece. "Surprise, people!"

"Lily? This is a surprise," said Dr. Kaplan, rolling down the window.

"Like, what are you even doing here?" Darrell asked.

"Like, nice to even see you, too," Lily said, snapping a picture of Darrell on her cell phone. "Oh, I'm posting that face." Her thumbs flew over the phone while she talked.

"I'm supposed to be on vacation with my parents in Paris right now," she said. "That's in France. One of my school friends was even coming with me. We were going to shop. Well, I was going to shop. Big-time. But then Mom got the flu. Also big-time. Then Dad had to fly to Seattle for work. So good-bye France, and that's why he called you, Uncle Roald, and . . . wait. You did talk to my dad? He said he was going to call you."

Dr. Kaplan frowned. "I . . ." He fished out his cell phone and tapped it several times. "It must have run out of battery. I'm so sorry I didn't get his message."

Lily clucked her tongue. "No one should ever let his battery run down. I never let my battery run down. Your phone is like your brain. More important, even. Anyway, my dad dropped us here for the week and-ta-da!-here we are."

Something sparked in Wade's head. "Us? We? Here we are?"

Lily turned and made a little wave toward the house. "Becca came with me. Wade, you remember Becca, right?"

Of course he did.

Becca Moore.

The instant Becca walked out of the shade of the overhang, Wade stood up like a soldier at attention. He couldn't stop himself. It was instinctive and weird. He knew it was. But more than being weird, it hurt, because Wade was still in the car. You don't stand up in cars. Even convertibles, which his dad's car was not. As Wade jammed his head into the ceiling, he knew it must look epically dumb.

Guys didn't stand up for just anyone.

But then, Becca Moore was not just anyone. She was . . . interesting. His brain wouldn't let him go any further than that.

Interesting.

Becca was born in Massachusetts and had moved to Austin when she was eight. She was tall and fair and had long brown, almost black hair tied in a loose ponytail. Wade was a little afraid of her because she was so smart, but she didn't broadcast it and was almost as quiet as he was, which was another cool thing about her. As she walked over to the car, she was wearing a faded red 2012 Austin Teen Book Festival T-shirt, slim blue jean leggings, and mouse-gray ballet flats so soft they made no more sound than if she were barefoot.

Interesting.

Dr. Kaplan got out of the car and hugged both girls. "Well, we're glad to have you visit. Come on in!"

Darrell couldn't stop laughing as Wade unfolded himself from the car and limped to the front door.

No sooner had they all piled inside than Lily spun around. "Pose!" She snapped another picture with her phone. "So awesome. Wade with his eyes closed. Darrell looking like . . . Darrell." Then she found a seat in the living room, tugged a sleek tablet computer from her bag, and instantly began to type on its touch-screen keyboard. She looked up. "I'm writing a travel blog. But you knew that, right?"

No one knew that. If Wade had realized he would end up on the internet, he might have combed his hair that morning. Or washed it.

Lily grinned as she typed. "Vacation Day One. The Big Disappointment. A week with my cousins Wade and Darrell. I can barely bring my fingers to type these words . . ."

Darrell frowned. "Ha. And also, ha."

Tearing his eyes away from Becca, who sat quietly on the couch next to Lily, Wade watched his father move distractedly around the living room. The coded email from Uncle Henry was obviously on his mind. Of course it was. Code? What did code even mean, except keeping a secret from someone? Who would Uncle Henry and his dad need to keep secrets from?

When the snappy conversation between Lily and Darrell finally paused, he spoke up. "Dad, the email?"

"I need your celestial map," his father said, as if he'd been waiting for a lull, too. "The star chart Uncle Henry gave you when you were seven."

Wade blinked. "Really? Why?"

"You'll see," his father said.

Chapter Five.

In the quiet of his room, Wade slid open the top drawer of his desk. He removed the leather folder as he had the night before. The map, so precious and so rare, would now, suddenly, be the center of everyone's attention. But why did Dad want the chart? Puzzling over this, he brought it into the dining room, where he found them all sitting around the table.

His father pulled out a chair for him. "Wade, open the map, please . . ."

He unzipped the folder and opened it flat, revealing the thick sheet of parchment creased over itself twice. He saw, as he hadn't in the darkness of his room the night before, faint, penciled letters on the backside, reading, Happy Birth-day, Wade. Carefully, he unfolded the parchment on the table and spread it out faceup.

Becca leaned over it, her eyes glowing. "Wade, this is so gorgeous. Wow . . ."

"Thanks," he said quietly.

Spread out, the map was about the size of a small poster. It had been engraved in 1515 and was exquisitely hand painted. The heavens were colored deep blue, and the original forty-eight constellations described by the ancient Greek astronomer Ptolemy were drawn and starred in silver inks. Crater, Lyra, Orion, Cassiopeia, all the others. Evenly spaced around the map's edge was a sequence of letters in gold forming an incomplete alphabet, which had always puzzled Wade and about which his father had offered no real explanation.

"Okay, so," Dr. Kaplan said, taking a deep breath. "First we have the email." He produced the printed email from his blazer pocket, then carefully traced his fingers over the letters bordering Wade's star map. "Uncle Henry gave you this chart for your birthday, knowing you would like it."

"I love it," Wade said almost reverently. "It's what really got me super-interested in the stars."

"I know," his father said. "Maybe you don't remember me telling you, but it wasn't the first time I had seen this map. Heinrich showed it to me while I was still a student, quite a few years before you were born. He had a little apartment then; he still does."

"Have you seen him since then?" Becca asked.

"Once, then letters, email once in a while," he said. "Heinrich had always been a collector of antiques. One night twenty or so years ago, in front of me and some other students, he unfolded five identical printings, all hand-colored, of the same map from the sixteenth century. This map. As we all watched, he took out a pen, dipped it in gold ink, and without a word, inked an alphabet around the edge of each one."

"But the alphabet is messed up," Lily said. "It's only got . . . seventeen letters." On her tablet she typed in the gold-inked letters framing the star map, while Darrell did the same on a yellow pad.

C D F G H I J K M O P Q V W X Y Z.

"Of course." Dr. Kaplan slipped on a pair of reading glasses. "We noticed the same thing. Heinrich told us our alphabets were one part of a cipher-a code-of his own invention. He said we might have to use it someday. Before we ever needed it, he said, he would see that we each received one copy of the map. Then he put them away before we could really do any figuring. And that was that. I never thought much about the maps again until your seventh birthday, Wade, when he gave you this one. He brushed off any mention of the code then. I assumed it didn't matter anymore."

Darrell shook his head slowly. "But it does matter. And it proves I was right. He was a spy. He was pretending to be a professor, but he was a secret agent."

Dr. Kaplan cracked a smile. "I really don't think so. He's retired now, but he was one of the foremost physicists of his day. When he first showed us the maps, he swore us to secrecy. He called our little group of five students Asterias. That's the Latin name for the sea star. We were, Heinrich said, like the five arms of the starfish, and he was the head. It seemed a little silly at the time. A professor's whimsy. But we were graduating and going our separate ways, so we all agreed. In the last few years I lost communication with most of them, and he's never asked me to use the code. Until today."

Wade breathed in to try to calm himself. It didn't work. A hundred questions collided in his brain. "Are you saying that the cipher on the map will decode the email?"

"But not all the letters are there," said Becca. "If it's a standard substitution code, it needs all twenty-six letters."

Everyone looked at her.

"Substitution code?" said Darrell. "Uh-huh. Putting aside for a moment what substitution codes even are, how do you know about them?"

Becca blushed a little. "I read. A lot. Last summer I read all the Sherlock Holmes stories. You know what I mean, right, Dr. Kaplan?"

He smiled. "I do. Sherlock Holmes solves substitution codes in several of the stories. When we asked Heinrich about the missing letters, he just winked and slyly tapped the side of his nose. We pressed him about what he meant, and he said, 'when things are missing, you look for them!' You're all pretty brainy, so the first step for us is, what letters are missing?"

Lily had apparently already figured it out and told them with a grin. "A, B, E, L, N, R, S, T, and U!"

"Good," Dr. Kaplan said. He wrote them on Darrell's pad.

A B E L N R S T U.

"Nine letters. The cipher begins as a fairly simple Caesar code, a substitution code originated a couple of thousand years ago by Julius Caesar for his private letters. Heinrich was a student of ciphers, and he modified this in his own way.

"So, the letters not on the map form a secret word or phrase. You unscramble the missing letters to find the words, then put them at the beginning of the alphabet to make the full twenty-six letters again."

"Nine letters could spell a lot of words," said Darrell.

Dr. Kaplan nodded. "But they should somehow be familiar to the person for whom the code is intended . . ." He paused, stroking his chin. "My diary. I kept a journal then, a student notebook, where I wrote down lecture notes and random things. It's in my office. Hold on." He left the room at a trot.

"We can start," said Becca. "A, B, E, L, N, R, S, T, and U. Let's think."

The dining room went quiet, except for Darrell's pencil scratching and occasional humming and Lily's fingers tapping on the tablet's screen. Becca frowned and looked off across the room.

Wade tried to think, but the image of Uncle Henry inking the maps in gold was mesmerizing. Was it by candlelight, their student faces glowing? Was his apartment as hushed as their dining room was right now? Why did he do it in the first place?

His father returned, leafing through a small black notebook. "Maybe the answer is somewhere in here . . ."

"I get the words rest, nut, and eat," Darrell said finally.

"Of course you do," said Lily. "I see ears."

"I get lean burst," said Becca with a smile. "Do I get a prize for using all the letters?"

Wade resisted jumping up and shouting, "Yes, you do!"

But the more he studied the letters, the more they began to shift places like the panels in one of those number slide puzzles. This was how his mind often solved math problems. His father said he was a natural at numbers. And now, apparently, at letters, too.

Common combinations . . . S . . . T . . . slid forward and back . . . vowels moved and moved again. Fixing his eyes on the letters, Wade went through them again, again, then click. Solved. Or sort of solved. He cleared his throat. "Well . . ."

Four faces looked at him.

"One thing the letters spell is blue star with an extra n," he said. "I don't know what the n stands for, but a blue star is a real thing. If a star appears blue, it means it's approaching Earth."

Dr. Kaplan stared at the letters on the pad, nodding. Then he turned to the last page in his notebook and smiled. "Oh, boy. Close. Very close. But look."

As they watched him, he slowly rewrote blue star n as blau stern.

"Blau stern?" said Becca. "That's blue star in German."

"Exactly," Dr. Kaplan said, showing them the words in his notebook. "Blau Stern was the name of the cafe in Berlin where we met after classes-"

"I knew it!" said Darrell. "Your spy hangout!"