London, 1853: Having earned some renown by solving a case that baffled Scotland Yard, young Charles Lenox is called upon by the Duke of Dorset, one of England's most revered noblemen, for help. A painting of the Duke's great-grandfather has been stolen from his private study. But the Duke's concern is not for his ancestor's portrait; hiding in plain sight nearby is another painting of infinitely more value, one that holds the key to one of the country's most famous and best-kept secrets.