“Grumpy,” said Tess, tossing the crust of her bread to Nine. But she turned her attention to Jaime’s sketchbook with the sketch of Ada’s letter. “Okay, what do we have?”

The puzzle fit in the palm of my hand. Made of silver and gemstones. I believe I left it in the M.s’ drawing room. I wonder if that empty-headed little girl with the yellow hair stole it. She was clutching her reticule quite tightly when she returned to the table, if I recall.

If she doesn’t melt it down out of sheer frustration, I can imagine she will deposit it in a spare box in her attic, to be found by a descendant and displayed in some museum or another a hundred hundred years from now. One more mysterious relic among many.

Oh, we have much work to do to, Mr. Babbage. Much work.

Yours,

A.A.L.

FCHBMFWSHFUVWSXLJSMCBHWJU

“We have some drawings of a cube, some sort of puzzle box. And some talk about it being stolen in 1844. And there is this string of characters along the bottom, which could be a cipher,” Jaime said.

“I wonder if we’re supposed to be solving this cipher or looking for this puzzle box.”

“Or both,” said Jaime.

“Or neither,” said Theo.

“You know it’s totally okay to stop telling us our ideas are stupid,” Tess said.

“When did I say that?” Theo said.

Tess sighed so hard a loose spiral of hair flew up, then floated back down to rest against her temple. “Let’s start with the cipher along the bottom. Maybe it’s something we can crack,” she suggested. The three of them looked at the string of letters and then they all took another cookie for fortification.

Jaime said what the three of them were thinking, and probably Nine, too. “If it’s just some word scrambled up, a substitution cipher, there are going to be so many possible permutations.”

“Millions and millions,” said Theo. But they tried it anyway, putting the characters into cipher solvers on the web, coming up with all sorts of meaningless words and phrases.

“Maybe the string of characters refers to something in the letter,” Tess said. “Like, say, the letter F refers to the sixth line or the sixth word of the letter, and so on.”

“There aren’t that many lines in the whole letter,” Theo said.

“The individual words, then,” said Tess.

They tried the sixth word. Palm. Then the third word, fit. The eighth, the second, etc.

“Palm, fit, my, puzzle, and,” Jaime said. “It doesn’t sound like it’s forming a new sentence as much as repeating what the letter already says.”

“We could try frequency analysis,” said Theo.

“What’s that?” Jaime asked.