He would unravel this mystery . . . or it would unravel him.

Captain Edmund Cholmely has been in the doldrums since his brother's exposure and death as a traitor. A coded ledger is stolen from the War Office, however, threatening to expose every secret operation Colonel Renforth's men have ever undertaken, not to mention other war secrets. The cipher is being used again and Renforth sets Edmund to discovering who has the code, seeing it as an opportune task with which Chum might break his melancholy. Edmund follows the leak to a seaside town where a reserved widow keeps a school, mostly for the daughters of naval officers and those wounded in the war. Her husband created the cipher . . .

Elise Larkin, widow of Captain Charles Larkin, has run a boarding school for the young ladies of naval officers ever since the loss of her husband. When the stranger comes to the village, she is torn between fear of his purpose and an attraction she cannot deny. Elise is one of just two people still alive who her husband entrusted with the key to a cipher he created for sending coded messages, and she is afraid it will be used for ill.

Edmund knows that recent messages have surfaced using the highly secretive code which is supposed to be dormant. Does the widow know the cipher or hold the key? If released, documents and informants' names could be revealed, putting them at risk. A mutual need to discover the truth throws Edmund and Elise together, but she suspects him and he suspects her. Gradually, however, Edmund's rigid notions of guilt and loyalty crumble. He must decide whether love requires trust even when honor forbids it.