Lady Miranda Hawthorne acts every inch the lady, but inside she longs to be bold and carefree. Approaching spinsterhood in the eyes of society, she pours her innermost feelings out not in a diary but in letters to her brother's old school friend, the Duke of Marshington. Since she's never actually met the man she has no intention of ever sending the letters and is mortified when her brother's mysterious new valet, Marlow, mistakenly mails one of the letters to the unsuspecting duke.

Shockingly, this breach of etiquette results in a reply from the duke that soon leads to a lively correspondence. Insecurity about her previous lack of suitors soon becomes confusion as Miranda finds herself equally intrigued by Marlow, a man she has come to depend upon but whose behavior grows more suspicious by the day. As the secret goings-on at her family's estate come to light, one thing is certain: Miranda's heart is far from all that's at risk for the Hawthornes and those they love.