Theo said, “The D could also represent a vowel. Like an O. But that’s only if this is a transposition cipher and not a substitution cipher. I think we have to assume it’s both, though. Maybe with more than one cipher alphabet.”
“Sometimes listening to you guys talk is like listening to strange music from a foreign country,” Jamie said. “Weird and interesting, but not something everyone can dance to.”
“In a transposition cipher, you basically take the letters in your message and just mix them up according to some pattern or scheme,” Tess explained.
“Yes. But in a substitution cipher, you substitute each letter for some other letter in a cipher alphabet. It used to be that people would use one cipher alphabet to encipher a message,” said Tess.
“Julius Caesar did a lot of this,” said Theo.
“It’s amazing how often people like Julius Caesar come up in conversations with you guys,” said Jaime.
Theo said, “Julius Caesar encrypted his messages with an alphabet that shifted three places to the left, like this.”
Theo wrote:
Jaime said, “So, you just stick A, B, C at the end, which stand in for X, Y, and Z?”
“Right,” said Theo. “If I wanted to use the Caesar shift to encrypt the word high, I would write KLJK.”
Tess said, “But it turns out that this kind of encryption is easy to break.”
“For who?” said Jaime.
“So people had to come up with something that was harder,” said Theo. “You want something hard to break, but easy to translate if you know the way the message has been encrypted. You could make up a cipher alphabet by jumbling up the letters of the alphabet, but unless the person you’re sending the message to has an exact copy of the cipher alphabet memorized, they won’t be able to figure it out.”
“Couldn’t a computer do it?” said Jaime.
“I guess, but if the cipher alphabet was totally random, there are something like four hundred septillion possible keys.”
“Even if you could check one key every single second, it would take a million times the lifetime of the universe to go through all of them,” said Tess.
“A billion times the lifetime of the universe,” said Theo.
“Million, billion, whatever,” said Tess.
Theo ignored her. “But let’s say the cipher alphabet wasn’t totally random, that you jumbled the letters using a certain key word or phrase. Like—”
“Julius Caesar!” said Jaime.
“—Ava Oneal,” said Theo. “You write out the key phrase, taking out all the spaces and any repeated characters. Then after that, you write the rest of the alphabet in order.” He wrote:
“Well, if the key were Ava Oneal, instead of A, D, G, L, M, R, S, Z, we’d have A, E, C, I, J, R, S, Z. That doesn’t seem to work. Three of the letters aren’t even ciphered.”
They tried Morningstarr for a key. They tried Old York Cipher and then just Cipher. For the heck of it, they tried Theresa and Theodore, Octagon, and Ava.
The smell of the pastelitos filled the apartment, rich and sweet and doughy. Tess’s mouth watered. Jaime’s stomach growled.
Jaime said, “What if it’s just a bunch of letters jumbled around?”
“We could try anagramming them. A computer might help us. Still an insane number of permutations, but maybe we’ll get a hint from an anagram solver site,” said Theo.
Jaime pulled his phone from his pocket and handed it to Theo. Theo found a site and entered ADGLMRSZ. “Nothing,” Theo said.
“What if that blank space is a vowel?” said Tess.
Theo tried that. Again, nothing.
“Look at the answers that contain only some of the letters. Maybe a partial answer will give us a clue,” said Tess.
“I have dogma or a dog. Molars.”
“Speaking of chewing,” said Jaime as his grandmother placed a tray of pastelitos and three glasses of milk on the table.
“Oh, Mrs. Cruz, these smell so good I could eat the air,” said Tess.
“I hope you will eat the food instead,” said Mima. “That is the normal thing to do.” She studied their notes, leafed through the pages with all the permutations of the letters, the different keys and alphabets. “You said this Rastafarian cipher—”
“Rosicrucian,” Theo said.
“This language of dots,” continued Mrs. Cruz, “was used by silly men in silly clubs. What about the guild that runs the Underway? They are silly. They don’t have any women. And they have secrets to keep, no?”
Theo said, “People have been questioning the Guildmen for more than a hundred years. They’re not talking.”
Jaime dropped his pastelito. “Mima, you’re a genius!”
“Yes, but what’s your point?” said his grandmother.
Jaime grabbed his phone, punched something in.
“What?” said Tess.
“A, D, G, L, M, R, S, Z isn’t a cipher at all.” Jaime flipped the phone so they could see. “These are train routes. All of them are train routes.” He pointed to the spill of coinlike seals on the table. “And these are tokens.”
CHAPTER TWENTY
Tess
Of course Theo asked his usual robot questions: Trains? (Yes, trains.) Where are we supposed to ride them? (Until we find out why we’re doing it.) Should we take Nine? (We’ll leave her with Mrs. Cruz for this one.) How can we be sure of this? (We can’t.) But what do we do once we’re on the trains? (We’ll pay the Guildmen.)
“Mrs. Cruz gave us the hint,” Tess said. “They’re the ones the Morningstarrs charged with the secrets of the Underway, right? And the clue in this building points to the Underway. I think they’re keeping the secrets of this clue.”
“People have asked the Guildmen about the Morningstarrs before,” said Theo.
“Maybe they didn’t ask the right questions,” Jaime said.
“What are the right questions?”
Jaime added a few more lines to whatever he was sketching. “Or maybe they didn’t understand the answers.”
“Who says we’ll understand the answers?” said Theo.
“We have the tokens,” Tess said.