A Letter to a Lady by M. P. Harding
Kenley Alcott has fallen ill with the worst affliction that a single man of marriageable age can have: loneliness. When he thinks about attaining a wife there is really only one woman he can consider—his best friend’s older sister. Drunk and lonely, he writes her a letter proposing marriage.
Lillian has just attained the greatest victory of her life; she has convinced her family to allow her to set up her own household and abandon the marriage mart. She can plan her life whatever way she wants. She’ll get a little cottage, learn how to bake, even find a lover. One more social season, and then she can embrace the life of a spinster. She can’t wait.
Then the letter comes.