Her Royal Spyness is a series of 5 novels until now.
The movie doesn't have a distributor or cast yet but here is what the author, Rhys Bowen, is saying about the leading role:
Set in London in 1930, this merry first in a new cozy series from Agatha-winner Bowen introduces a delightful heroine—Lady Victoria Georgiana Charlotte Eugenie. Thirty-fourth in line for the English throne, Georgie has been educated to curtsey, host lavish fetes and marry well. When her brother cuts off her pitiful allowance, Georgie leaves the family home in Scotland for London, determined to become a liberated woman. Lasting only a few hours as a saleswoman in Harrods, Georgie starts a maid service, but she turns detective after finding a drowned man in her bathtub. When her brother is accused of the murder, she must try to clear him and the family name. Quirky characters like her lovable grandfather; her estranged, oft-wed mother; and an incorrigible, sexy Irishman add to the fun. Georgie's madcap antics are certain to leave the reader eager for the next installment.
The movie doesn't have a distributor or cast yet but here is what the author, Rhys Bowen, is saying about the leading role:
I had a very heady Hollywood moment when Her Royal Spyness was optioned and I had lunch with the producers and they asked me what my feelings were about Keira Knightley. We actually came to the conclusion that Emma Watson might be a better bet. As yet the project is moving forward, so they say, and an English production company is on board but we haven't got to the casting stage. It's all pie in the sky and rather fun in the abstrac.
Source: Pottershots
EDIT: TheCoffeeBreak emailed Rhys Bowen for more explanation and here is her answer:
She would be one of my top choices. I don't believe it's reached that stage yet. They are still refining the script before it can be sent to potential stars. As soon as I have any news I'll share it, I promise.
Best Rhys Bowen.