The King Was in His Counting House - Daniel McCoy

A South London chancer stumbles across a hundred year-old mystery when a rich and beautiful woman asks him to find her missing husband. He finds himself in a world he barely understands, of cryptography and cryptic puzzles, of secret funds and great power politics. And most puzzling of all, what was the connection between a murder, a small, exclusive bank and what one royal biographer described as the most perplexing act of a king's reign: "The abandonment of a loyal ally and much-loved cousin to degradation and death"?