William Clarence Verity, Sergeant in 'A' Division of the Metropolitan Police, has seen most of the horrors of the nineteenth century, from the stews of Seven Dials to the prisons of the maharajahs. Now he is sent to the United States, to a nation on the brink of civil war, to guard two of his country's most precious possessions: her good name, and the heir to the throne.

Both are threatened by Verney Dacre, thought to have died in the aftermath of the Great Train Robbery of 1857, but planning a coup to crown his career of evil: the robbery of the US mint in Philadelphia.