A saboteur on Columbus's Santa Maria. A girl with the voice of a split Berlin in her ears. A communist agent undermining a fascist MI6. Spies can change the course of history, and and in the six thrilling stories of Substitution Cipher, they do. Each tale follows its agent through a world that could have been ours, if not for one crucial difference: a clockwork Venice, a Germany marching north instead of east, a city too powerful to silence. And at the heart of each story is the sense of how easily - and how eerily - the world can be changed.