“I am sorry you are frustrated.”

“It’s fine,” I said again, and then because it wasn’t fine and there was no one else to let off steam to, I went on, “It’s only that she’s changed the game. She based the stupid cipher on a card game, and I had it sorted out, but now she’s gone and changed the game, I think, and I can’t figure out to what.”

He blinked at me a moment. Then he simply said, “OK.”

It was the best thing anybody could have done to break my mood. He sounded so exactly like his father that I couldn’t help but be amused. I said, “You didn’t understand that, did you? Any of it?”

Noah shook his head.

I switched to French, and in less aggravated terms explained the problem.

“Oh,” said Noah. “Can I help?”

I nearly told him no, he couldn’t help at all, he was too young to be of any proper use to me…and then in time I caught myself, recalling that it had been Noah’s offhand mention of discarding cards that had been key to my decrypting Mary’s cipher in the first place, so I said, “All right.”

I’d read in books of people “lighting up” when they were happy, but I’d never had a sense of what that meant, because a person couldn’t really light up. But the change in Noah’s features when I told him he could help me made him seem more animated. Brighter. Maybe that was what the books were on about.

I shifted my chair to the side so he could come and stand beside me. “See this list? It’s all the different card games people played back in the early eighteenth century. The time when this cipher was written.”

“Where did you find these?”

Why did children ask the most inconsequential questions? “On the Internet. Now, I’ve got through this list to here,” I said, and pointed to the place. “So when I ask you to, just read me the next game that’s got a star beside it, and then tell me what the numbers are beside that name, all right?”

“OK.” He took the list into his hands, a move that shifted the black cat held in his arms so that Diablo’s face was level with my own. It was a little disconcerting being stared at by a cat, and definitely not my normal solitary working pattern, but at least I’d lost the anger and could turn my focus fully on the task at hand.

“All right,” I said to Noah. “Read me out the next one.”

“Whist,” he told me, with exaggerated emphasis upon the wh so that it came out: “Wuh-hist.”

“And the numbers?”

“Two and twelve.”

I set to work with those.

“I like this other name,” said Noah. “Lanterloo. It’s funny. It’s a funny word to say.” As though to prove it, he repeated “Lanterloo” in different tones at different speeds.

I interrupted him. “You did say you would help me, yes?”

“Of course.”

“Well, that’s not helpful. Does it have a star beside it?”

Noah peered down at the list. “No.”

“Then it isn’t one we need to know.”

“What does the star mean?” Noah asked.

I wasn’t used to having someone asking questions at my shoulder while I worked. “It means that cards are taken from the pack before they start to play that game. Like in belote.” I realized that he didn’t know the help he’d been to me already, so I told him how his comment New Year’s Eve had set me on a course to solve the cipher.

He was smiling. “Really? Did I really help you?”

“Yes. Perhaps you’ll be a spy when you grow up.”

“I wouldn’t like to be a spy. They’re like assassins,” Noah said. “They can’t have friends.”

The perfect sort of job for me, then. “Is that right?” I only said this because Jacqui always said it, I had noticed, when she was absorbed in something else yet wanted to appear to be involved in someone’s conversation. And it worked. While I was focused on my numbers, Noah rambled on about some comic book, and I paid no attention. When I’d finished, he was finishing as well.

“…so it was only that his family had been killed and he was left alone and that’s why he became a hit man, but he wasn’t really bad.”

“That’s nice,” I said. “The next one, please.”

“Why do you only want the games where they take cards out first?”

One saving feature of his questions, I conceded, was the fact they were direct enough that I could answer easily. “Because she used a game like that to be her key the first time round. It makes the cipher trickier. I’m guessing she’ll have made another game like that her key this time, as well.” If I was wrong, I thought, at least I’d have eliminated several possibilities among the many. Evidently people in the eighteenth century had loved their card games.

Noah frowned. “A key like in the door?”

“In a way. A door key can unlock a door, a cipher key unlocks the cipher, but it doesn’t look the way a door key looks. In this case it would be a piece of paper, where she wrote a list to show what number stands in for what letter.” Which was simplifying things, because of course some ciphers used more complicated keys.

“Why,” asked Noah, “is it called a cipher?”

In his arms the cat had changed position, rolling so his head was upside down but with his gaze still steady on me as though he was also interested.