July 1794, and the streets of London are filled with rumours of revolution. Laurence Jago - clerk to the Foreign Office - is ever more reliant on the Black Drop to ease his nightmares. A highly sensitive letter has been leaked to the press, and Laurence is a suspect. Then, he discovers the body of a fellow clerk, supposedly a suicide. Blame for the leak is shifted to the dead man, but Laurence is certain both of his friend's innocence, and that he was murdered. But at a time when even the slightest hint of treason can lead to the gallows, how can Laurence find the true culprit without incriminating himself?
