The Amersham Rubies, by Rhys Bowen, is free to pre-order in the Kindle store. It looks like it will be a short story/novelette, but there isn't enough information to really tell, at this point (it might even be a full novel, although it doesn't appear to be so, from reading the limited info the author has put out on it.).
Book Description
Before Molly Murphy crossed the Atlantic or even had an inkling that she might someday become a much sought after private investigator in New York City, young Molly lived in Ireland in a small cottage with her father, brothers and little else.
While keeping herself and her home together, Molly receives a request from Lady Hartley—the lady of the country estate where Molly lives, and the family that employs Molly’s father and brothers. The Hartleys are hosting a ball at their manor house, and there will be so many fine gentlemen and ladies in attendance that Lady Hartley needs Molly to help some of her guests prepare for the ball.
Beautiful debutantes, dresses of the finest fabrics, and sparkling chandeliers are all on display, as are heirloom jewels like the Amersham rubies—a stunning and priceless ruby necklace that has been in the Amersham family for generations. When the rubies go inexplicably missing from Lady Amersham’s neck in the middle of the party, the high-spirited Molly must rely on her wits to solve her first case in Rhys Bowen’s charming prequel to her beloved Anthony and Agatha Award–winning historical mystery series.