1786, England

It is the twelve days of Christmas, and Mrs. Tiffany Lathrop is happily juggling her duties as a new mother and a librarian to Catharine, the Duchess of Beaufort. Her employer receives a mysterious letter from an old paramour, the Marquess of Harwood, who is the biological father of Catharine's son. He promises to leave his estate and fortune to Beau if he can see the boy before he dies.

Her elder son, Thomas Montague, has a terrible cold, so Catharine asks Tiffany to accompany her and Beau. When they arrive at the dilapidated abbey, they discover a dead body—only it isn't the marquess, but his valet! Lord Harwood is alive, but unconscious with suspicious-looking pox marks on his hands. Tiffany wonders if the marquess is really dying, or if it is all poetic revenge? Especially when she discovers the secrets that haunt Rosedean Abbey.

Between breastfeeding and dirty diapers, Tiffany must discover who killed the valet and attempted to murder the marquess before anyone else dies.