“Judging from the script in the Psalter I would have said early sixteenth century—almost certainly at the time of the Reformation. For a medieval manuscript, it’s young.”
“But for a complex cipher, it’s old,” said Oscar. “Most medieval ciphers are what’s called simple alphabetic substitutions. Each letter of the alphabet is substituted by another letter of the alphabet—so A becomes X, for example, or B becomes W. On the surface, that’s what this looks like, so it should be pretty easy to crack.”
“How do you do it?” said Arthur, settling into a chair across from Oscar.
“Frequency analysis,” said Oscar. “You look for the most frequently recurring letters and try substituting the most common letters in the language that’s been enciphered. In English that would be E, T, A, and O. On the other end, you look for rarely occurring characters and those are likely to represent Q, X, and Z. I’m assuming this text is Latin, but I can’t get anywhere with frequency analysis.”
“Could it be something older than Latin? Saxon?”
“Possibly,” said Oscar, “but that would present a whole different set of cryptographic challenges—this is written in the Roman alphabet; I’m not sure how you would encrypt the Saxon alphabet into Roman. For that you’d need a linguist; I just do maths. But if it’s fifteenth or sixteenth century, it’s almost certainly Latin. Nobody was reading and writing Saxon by then.”
“True,” said Arthur.
“Well,” said Oscar, pushing the pages across the desk to Arthur, “I leave you to it. I have a student to tutor at ten and then it’s back to the hospital to see Mum. There’s a chance they might let her go home later today.”
“I’m afraid I’ll be rubbish at this,” said Arthur. “Maths was never my strong suit.”
“Take this,” said Oscar, handing Arthur a slim paperback. “This isn’t the Enigma code. Anything encoded in the fifteenth century we should be able to break, even if it turns out to be polyalphabetic—but that seems unlikely for Britain.”
“Polyalphabetic?” said Arthur, feeling more confused by the moment.
“It’s all in the book,” said Oscar. “It’s a basic guide to simple ciphers and cryptanalysis. You’ll be an expert by this afternoon.”
“I doubt that,” said Arthur, picking up the book.
“Bonam fortunam!” said Oscar, and he was off.
—
Three hours later Arthur was bleary-eyed with confusion. He had read all about simple substitution ciphers without learning much more than Oscar had already told him. He had pored over the section on polyalphabetic substitution—which worked the same way as simple substitution but used multiple alphabets. This did not come into use in Europe until the sixteenth century, shortly before the time Arthur believed the Barchester manuscript was encoded. He had tried to understand transposition ciphers, which had to do with shifting the positions of the letters according to some regular pattern; none of the patterns suggested by the book yielded any results when applied to the pages of the manuscript. Annoyingly, in the description of each of these types of ciphers, Arthur found phrases such as “quite easy to crack” or “trivial to break.” Arthur was not fond of feeling stupid. He had before him the instructions for decrypting virtually any medieval cipher, and though he was no skilled mathematician, he could certainly follow instructions. But these instructions had produced a total of precisely nil. Once in a while a group of letters would transform itself into a word, but if he tried to apply the rule that had led to that metamorphosis to another group, it yielded gibberish. He had been excited at first by the idea of frequency analysis, because the letters U, Q, and D appeared much more often than any others, but no matter what substitutions he made, the results were always nonsense. Besides, most of the rest of the alphabet seemed pretty evenly distributed, except that letters at the end of the alphabet appeared quite rarely. But this whisper of a pattern didn’t lead him to any results.
He had just slammed the book on ciphers down on the table—not for the first time—when Bethany swept into the room. She wore a bright floral print dress that seemed to waft sunshine into the library.
“Good morning, my fellow conspirator,” she said. “That was an adventure last night, wasn’t it?”
“More of an adventure than I’m used to,” said Arthur. It had taken him hours to get to sleep—he assumed because adrenaline was still coursing through him.
“It’s good for you, old man,” said Bethany. “So how was your morning? Because my morning was amazing. First of all, I decided I’m going to have to start getting more exercise than one gets in manuscript heists if I’m going to eat any more full English breakfasts, and I have to say, I’m a fan. So I took a long walk this morning. Did you know that if you go straight up St. George Street out of town you get to the top of this hill in a mile or so with an amazing view of the whole city? The cathedral looks like a little toy church and the river was a ribbon of sunshine cutting through the meadows. Have you ever been up there?”
“I thought you wanted to know how my morning was,” said Arthur.
“I do,” said Bethany, “but we’re doing mine first.”
“In that case, yes, I’ve been there often. It’s lovely.”
“What are those ruins up the river outside of town?”
“That’s the Priory of St. Ewolda,” said Arthur.
“Of course,” said Bethany.
“I’ll take you there sometime,” said Arthur, pushing the manuscript away and turning his chair around to face Bethany, who had ceased puttering around the room and was now seated. How was it that she could smile like that? he wondered. He hadn’t thought about it before, but she almost always smiled. And it was the sort of smile one couldn’t ignore. He had seen it with the old man in the rest home, and with Oscar and David—Bethany had a way of making other people happy just by her presence. It was remarkable that, with a centuries-old mystery on the table and thousands of rare books and manuscripts surrounding him, what he wanted to do more than anything else at this moment was listen to Bethany natter on about the meaningless minutiae of her morning.
“Anyway, that view was just the first cool thing to happen this morning. I had breakfast with Gwyn, and guess what? She has actually seen the Nanteos Cup.”
Arthur sat up in his seat. “You’re kidding. I can’t believe she never told me, knowing how much I like . . . old things.”
“She didn’t tell you because she knew you wouldn’t believe,” said Bethany. “Remember the story of Mrs. Mirylees, who owned the cup? She didn’t want to have it scientifically tested because she thought people’s belief in the cup was more important that anything tests would prove. The Grail is about faith, Arthur. Anyway, Gwyn grew up in Wales and when she was eight she was riding her bicycle through the village and was hit by a car. She was in a coma for two weeks and apparently her mother knew the woman who owned the cup and she asked if she could have some water from the cup for her daughter. Ten minutes after the water touched Gwyn’s lips, she woke up.”