“Looks like something out of The Da Vinci Code.”

Harris chuckled. “Ol’ Leonardo would have been fascinated by the next evolution of the wheel cipher.”

He dragged her over to another display case containing several machines that looked like big typewriters.

She read the placard. “Enigma cipher machines,” she said with excitement in her eyes. “I’ve heard of them.”

“They were one of the best-kept secrets of World War Two. People would have killed for one of these contraptions. They were basically glorified versions of Jefferson’s wheel cipher. He was far ahead of his day.”

“Too bad we can’t use one of these things to decipher his writing,” Angela said.

“We may not have to,” Harris said.

They returned to Harris’s office, where he plopped behind the desk again. He leaned back in his chair and tented his fingers.

“How did you get into codes and ciphers?” he said.

“I’m good at math. I do the crosswords, and I’ve liked acrostics since I was a kid. My interest in puzzles got me into reading books on the subject. That’s where I read about cipher grilles and Jefferson’s interest in cryptology.”

“Half the cryptologists in the world would have given me the same answer,” Harris said. “It was exactly those interests that allowed you to sense the possibility of a hidden message in this stuff.”

She shrugged. “Something about it struck me as being funny.”

“‘Funny stuff’ is what the NSA deals with on a regular basis. Jefferson would have felt right at home in the agency.”

“Where does his wheel cipher fit it?”

“It doesn’t. Jefferson got away from cipher devices later in his career. My guess is that he only used the grille to create a steganograph to conceal the fact that the artichoke info contains a secret message. He would have jotted down the message in the apertures and built sentences around them.”

“I noticed that the syntax in the text seemed stilted or just plain weird in some of the lines.”

“Good catch. Let’s assume Jefferson used this as an extra layer of concealment. First, we’ll have to copy the letters exposed by the holes in the grille.”

Angela pulled a notebook out of her briefcase and handed it over. “I’ve already done that.”

Harris inspected the lines of seemingly unrelated letters. “Fantastic! That will save a lot of time.”

“Where do we start?”

“About two thousand years ago.”

“Pardon?”

“Julius Caesar used a substitution cipher to get a message to Cicero doing the Gallic Wars. He simply substituted Greek letters for Roman. He improved on the system later on. He’d take the plain text alphabet and create a cipher alphabet by shifting letters three places down. Put one alphabet over the other and you can substitute those letters on one row for the other.”

“Is that what we have here?”

“Not exactly. The Arabs discovered that if you figured out the frequency of a letter’s appearance in written language, you could decipher a substitution cipher. Mary, Queen of Scots, lost her head after Queen Elizabeth’s code-breakers intercepted the messages used in the Babington Plot. Jefferson developed a variation of a system known as the Vigenere method.”

“Which is an expansion of the Caesar substitution.”

“Correct. You create a batch of cipher alphabets by shifting so many letters over for each one. You stack them in rows to form a Vigenere box. Then you write a key word repetitively across the top of the box. The letters in the key word help you locate your encoded letters, something like plotting points on a graph.”

“That would mean that the letters in your clear text would be represented by different letters.”

“That’s the beauty of the system. It prevents the use of letter frequency tables.”

Harris turned to a computer and, after typing furiously for several minutes, created columns of letters arranged in a rectangular shape. “This is the standard Vigenere box. There’s only one problem. We don’t know the key word.”

“How about using artichoke?”

Harris laughed. “Poe’s ‘Purloined Letter,’ out in plain sight? Artichoke was the key word Jefferson and Meriwether Lewis used to unlock the code they agreed on for the LouisianaTerritory expedition.”

He wrote the word artichoke several times across the top of the square and tried to decipher the encrypted message revealed through the grille. He tried the plural form and shook his head.

“Maybe that was too obvious,” Angela said. They tried Adams, Washington, Franklin, and Independence, all with the same disappointing results.

“We could spend all day doing this,” Angela said.

“Actually, we could spend decades. The key word doesn’t even have to make sense.”

“So there is no way a Vigenere cipher can be broken?”

“Any cipher can be broken. This one was busted in the 1800s by a guy named Babbage, a genius who’s been called the father of the computer. His system looked for sequences of letters. Once he had those, he could figure out the key word. Something like that exceeds my skills. Fortunately, we’re within spitting distance of the greatest code breakers in the world.”

“You know someone at the NSA?”

“I’ll give my professor a jingle.”

The professor was in class, so Harris left a message. With Angela’s permission, he copied the material. He’d been so intent on the written text that he had paid little attention to the drawing.

Angela saw him studying the lines and Xs. “That’s the other part of the mystery. I thought it was a garden layout at first.” She told him what she had found on the ancient-languages website.

“Fascinating, but let’s concentrate on the main text message for now.”

Harris made copies of the papers. Angela tucked the original documents back into her briefcase. Harris walked her to the door and said he would let her know what he learned. Two hours later, he got a call from his professor. Harris started to tell him about the cipher problem. He only got as far as the name Jefferson when the professor told him to come over immediately.

Professor Pieter DeVries was waiting for Harris at the other side of the security check-in. The professor practically dragged Harris to his office in his haste to look at the file.

The professor epitomized the brilliant but absentminded mathematician that he was. He tended toward tweed suits, even in the warmer months, and had the habit of tugging at his snowy Vandyke beard when he was engaged in thought, which was most of the time.

He studied the artichoke file. “You say a young lady from the Philosophical Society brought this to you?”

“That’s right. She works in their research library.”

“I probably wouldn’t have given it a second look if not for the grille,” which Angela had let Harris hold on to. He picked up the perforated cardboard, stared at it with disdain, and then set it aside. “I’m surprised Jefferson would have used something as crude as this.”

“I’m still not convinced this stuff conceals a message,” Harris said.

“There’s one way to find out,” the professor replied.

He scanned the columns of letters into a computer and tapped the keyboard for a few minutes. Letters arranged and rearranged themselves on the screen until a word popped up.

EAGLE

Harris squinted at the screen and laughed. “We should have known. Eagle was Jefferson’s favorite horse.”

The professor smiled. “Babbage would have sold his soul for a computer with tenth the capacity of this machine.” He typed the key word onto the screen and then instructed the computer to use it to decipher the message he had scanned earlier.

The letter Jefferson had written to Lewis in 1809 came up in plain text.

Harris leaned over the professor’s shoulder.

“I can’t believe what I’m reading,” he said. “This is crazy.” Harris dug out the paper with the odd drawings on it. “Angela thinks these words are Phoenician.”