Lord John is in a difficult spot. His cousin Olivia is engaged to marry the Honorable Joseph Trevelyan, but he has just observed something of a rather personal nature that, if confirmed, might put an end to any talk of marital bliss. Determined to investigate further, Lord John is distracted when the Crown calls for his services. A comrade in arms has been slain, and to complicate matters, the victim may have been a traitor. Now Lord John has not one, but two puzzling mysteries to solve.