An extraordinary turn of events sees Marylebone cab proprietor, Henry Gough, propelled from the familiar streets of Victorian London into the grip of a stirring adventure, full of danger, political intrigue and ruthless treachery in faraway Siam.

When Henry becomes the only witness to the brutal murder of his passenger on one of London's richest avenues, he is given a clandestine mission to perform. It will end on the banks of Bangkok's steamy Chao Phraya River, where he uncovers a sinister plot that may bring chaos to Siam.

When Henry draws ever closer to revealing the assassin's true identity, he is forced to confront powerful forces that threaten his life. As Britain and France's colonial ambitions clash inside the court of Siamese King Chulalongkorn, the scene is set for a bitter struggle that will decide the fate of Siam itself.