London, 1926. Harris Stuyvesant, agent of the US Bureau of Investigation, is on a mission. A series of bomb attacks on American soil, thought to be enacted by an up-and-coming British politician, have left him with a vendetta more personal than professional. But when his search for answers leads him to government official Aldous Carstairs, the US agent may find himself in over his head.

At Carstairs' recommendation, Stuyvesant enlists the help of Bennett Grey, a man with unique abilities. After the Great War left him with an excruciating sensitivity to human deceit, Grey has withdrawn from the world. Now, however, he must help the American insert himself into the terrorist's rich and radical social circle. Here Stuyvesant uncovers hidden secrets, a horrifying conspiracy, and wonders if he can trust his touchstone, Grey, to reveal the most dangerous player of all . . .