Princess Elizabeth's Spy

that he’d stared at her through the plate-glass windows in the dark and cold, before finally leaving. The answers his daughter wanted from him—they just weren’t anything he could or would tell her. Even if it meant disappointing her. Even if it meant losing her again.

“Good,” Frain said. “Let’s keep it that way.”

Chapter Thirteen

Monday morning was Princess Elizabeth’s first maths lesson.

It was not going well.

“But Crawfie’s already taught me how to add, subtract, multiply, and divide,” Lilibet said earnestly in the nursery, warmed by orange and indigo flames crackling behind the brass fender. “And we’ve gone over decimals and fractions. I really don’t know what more there is.” A few of the corgis were napping in front of the fender on their needlepoint pillows, snoring. Dookie snorted and opened his black eyes for a moment, then went back to sleep.

Maggie smiled. “A bit more.”

“But it’s not as if I’ll have to do my own books,” Lilibet said, parroting what she must have heard Crawfie say.

“No,” Maggie rejoined, “but you may want to keep an eye on those books when you’re Queen.” She let Lilibet think about it. “Just a suggestion, of course.”

“Oh,” Lilibet said, considering. “Perhaps you’re right.”

“Actually,” Maggie said, sitting down next to the girl, “I thought we might do something different today. It’s math, but it doesn’t really have to do with numbers at all. And it does have to do with a queen. Two queens. And how math saved Queen Elizabeth’s crown.”

“Really?” At this, Lilibet perked up.

“Really.” And Maggie began to relate the story of how, when Mary, Queen of Scots, was on trial for treason, accused of trying to assassinate the Protestant Queen Elizabeth, and facing a death sentence, she’d used code to communicate with her fellow Catholics. “You see, Mary had actually authorized the plot to murder Queen Elizabeth. But all of her messages were written in cipher. In order to prove her guilt, Queen Elizabeth would have to break the cipher.”

Lilibet’s eyes were huge. “Yes?”

“Well, luckily, she had on her side a brilliant mathematician, Sir Francis Walsingham, her principal secretary. Walsingham was an expert at breaking codes and ciphers.”

“But what does this have to do with maths?”

“We’re getting there!” Maggie said, pleased that she now had her young charge’s interest. “Mary’s letters to her supporters were in cipher—and it would take maths, some pretty sophisticated maths, to break the code.” She got up, went to her bookcase, and pulled out a book about Mary, Queen of Scots, in which she’d bookmarked of one of Anthony Babington’s messages to Mary, written in code. “What do you make of this?” Maggie asked.

[Art TK Here]

“It’s … gibberish. Those aren’t even real numbers or letters.” She sighed in exasperation. “It doesn’t make sense.”

“Ah, but if you know maths, it just might. Not only was it a secret message about the assassination of Queen Elizabeth, written in code, but it, like their other messages, was smuggled in and out of prison through beer-barrel stoppers. Queen Mary’s servants would retrieve the messages from the beer-barrels and place messages back into the hollow of the stopper.”

“But how did they figure it out?”

“Sir Francis, Queen Elizabeth’s Royal Spy Master, intercepted all of the messages between Queen Mary and Anthony Babington. Each message was copied by the Spy Master and then sent on to its destination intact. Then Sir Francis decoded each message, using the frequency analysis—the frequency of common characters—until a readable text was found. The rest of the message was guessed at by the message context until the entire cipher was understood.”

“What’s—what did you say? ‘Frequency analysis’?”

“Well, think about the alphabet. What are some letters that are used most frequently in words?”

Lilibet considered for a moment. “E, of course. And some of the other vowels.”

“Yes!” Maggie exclaimed, gratified. “And what are some letters that aren’t used very much?”

“Well, Zed, of course. And X. And Q.”

“And Q always is followed by a—”

“U!” the Princess exclaimed.

“What Queen Elizabeth’s code breaker did was figure out which symbols Queen Mary used that appeared with the same frequency as letters of the alphabet. He proposed values for the symbols that appeared most often. By figuring out the symbol used most frequently, he could deduce it was an e. And so on. Using math and common sense, he was able to break the code.”

“Goodness,” Lilibet said. “It probably saved Queen Elizabeth’s life.”

“It did. And cost Queen Mary hers. Now—I have an idea for something fun to do.”

The princess looked wary. “What is it?”

“Well, how would you and Princess Margaret like to have your own ultra-secret code to communicate in? That no one, not even Crawfie or Alah, could read?”

“Oh, yes, yes, please, Maggie.”

“Then let’s get started, shall we?”

It took a while, but Lilibet created a cipher. Like Queen Mary’s code, it wasn’t just a simple monoalphabetic substitution and code words. Maggie had a decoder, a giveaway from a long-ago jar of Ovaltine. It might have been a toy intended for children, but it was a descendant of the cipher disk, developed in the fifteenth century by Leon Battista Alberti. The center wheel had a circle of numbers, which turned to match a stationary outer circle of letters.

Maggie gave it to Lilibet, who took it with a sort of awe, twisting the dial this way and that.

“The decoder—really a cipher disk—can be used in one of two ways,” Maggie said. “The code can be a consistent monoalphabetic substitution for the entire cipher—or the disks can be moved periodically throughout the cipher, making it polyalphabetic.”

“What?” Lilibet said, knitting her brows.

“Hmmmm …” Maggie remembered her young charge was only fourteen. “The sender and the person receiving the messages would need to agree on a cipher key setting. The entire message is then encoded according to this key. You also could use a character to mean ‘end of word,’ although this makes the code less secure.…”

Lilibet looked concerned.

“Oh, come on, we’ll make one up and then you’ll see how fun it is,” Maggie said.

After a bit of thinking and moving the rings, Lilibet dipped her pen in a bottle of Parker Quink Black and wrote her first note, in code, to Margaret. The code was set for the 1 to indicate the start of the alphabet, set at E, for Elizabeth. “+” was to indicate the end of a word.

And so, “Meet me in the garden” became “9 1 1 16 + 9 1 + 5 10 + 16 4 1 + 3 23 14 26 1 10”—and by twisting the dial, and remembering the E setting, Lilibet could get to the correct letters to spell out the message.

“May I go and show Margaret, Maggie? Please? It will make her laugh, and she loves to laugh so much.”

“Of course,” Maggie said. “We’re done for the day. And be sure to teach her how the code works, so she can write back to you.”

“Maybe I could use the code when I write to—” the Princess began. Then she stopped herself.

“Write to …?” Maggie prodded.

“Well,” Lilibet said, blush staining her cheeks, “there’s this boy we all know. His name is Philip.”

“Oh?” Maggie said. Her lips twitched as she realized Lilibet had a crush.

“He’s a bit older than I am, and in the Royal Navy. But we’ve been writing to each other. Mummy and Daddy