“But who shall bell the cat?” asked Jefferson. “Who is the spy that carried your message away into British hands this afternoon?”

“I’m afraid I had to suggest someone to divert attention,” Franklin said. “So I chose your father, Quincy. Please forgive me. In fact, it’s our secretary, Edward Bancroft. We have long followed his movements. Bancroft leaves Le Valentinois each Tuesday night and retires to the gardens of the Tuileries at the heart of Paris. There, at eleven-thirty, under cover of darkness, he deposits a packet of papers inside the hollow of an old oak tree—a packet containing all the intelligence he’s gathered from us in the week. The British Secret Service pays him five hundred pounds per annum to spy upon us, and we pay him to spy on them. It’s the only way we can be certain that the British are receiving the news we want them to know. When you, my dear Jefferson, replace me in this French mission, I pray you may find him useful!”

Jefferson laughed modestly. “As I often say, I can only succeed you—no one can replace you. It seems now you’re a master of the French art of espionage, too. But if that message was calculated to trick the British into thwarting a Jacobite plot, something remains unexplained. Why did you invite us to meet you in the gardens here tonight?”

At that moment, the carillon of water bells from Chaumont’s octagon pool began striking the hour of twelve. When the tones had died out, Franklin said, “Invite you? Why, to attend the salon of Notre dame d’Auteuil, of course!”

Mme Helvetius had stood all this time gazing down at the river. Now she said, “The Loge des Neuf Soeurs. They arrive with the water bells.”

Slipping from shadow on the river below, they saw a long boat rowed by nine sturdy men that was pulling toward the moonwashed pier.

“Nine muses, and a carillon of bells in E-flat major,” Franklin explained to Jefferson. “That is the missing code that you and young Johnnie here were seeking. In both versions of our ditty, one hears three chimes of the bell, three notes that are repeated: Din-Dan-Don…Ding-Ding-Dong. These three notes represent the Masonic code—the number three. Masonic songs are always written in E-flat major, containing a musical signature of three flats—with the E itself being the third note of the octave music scale. The repetition of the bell, three and three, represents three-squared, which is nine, reflective of the name of Madame’s lodge down there, filled with musings and dedicated to muses.” He laughed.

“But then, at last, as in any code,” Franklin added, “there is always that final question which explains all the rest.”

Jefferson had joined Mme Helvetius in gazing down at the nine men below, who had lashed down their boat and were disembarking on the pier. Despite the warm night, they were shrouded in black. For a time, no one beside the pool spoke. It was Jefferson who broke the silence.