“In my head I built a room, in which I kept the truths I dared not speak. And in this room sometimes I said, the kings will return no more to the Realm. Nobody dares say this, but everyone knows it is the Truth. In this room I said, it is good that the kings’ tyranny is gone forever. Men would hang me for saying so, but their hearts would whisper all the while that I spoke the Truth. And in this room I said that until the ordinary people choose their own leaders they will suffer, and this too is the Truth . . .”

The meaning of these words would have been lost on most children—and, for that matter, on many adults—but the eavesdropper in the cannon nook was Mosca Mye, who had begged and bartered for books and broadsheets all her life. This was radical talk—this dripped treason. The teacher below could be hanged for the words he was reading out. Mosca’s eyes glittered vengefully.

“In this little room of the mind the truths grew strong and strident, and I knew that I must speak them whatever the cost . . .”

There was a sharp whistle from somewhere directly below Mosca, and with a shock she realized that the boy she had chased had been standing with his back flat against the flint wall, keeping an eye on the street.

“Class dismissed,” declared the teacher sharply, slamming his bread shut with a small explosion of crumbs.

Five of the children disappeared through holes in the ruined wall, the smallest leapfrogging through on his hands. The eldest boy scrambled up the side of the nearest house, then hung his arms over the roof’s edge to pull up a smaller friend. Four others dropped to their knees and silently renewed their game of marbles.

The teacher pulled his cravat loose, and then retied it as he walked back toward the street. By the time he reached the mouth of the alleyway he was pulling it back into its bow, for all the world as if he had simply stepped into the alley to get out of the wind and set it straight. At the street corner he passed a tall gentleman in a full-bottomed wig who had just stepped into the alley, the reason for the lookout’s whistle, and nodded to him courteously.

Legs shaking with excitement, Mosca scrambled down the wall, and set off in pursuit of the treasonous teacher. Very soon she was learning a few harsh lessons about spying in a busy city street.