Her Royal Spyness by Rhys Bowen (2007)
In 1930, Lady Georgine is 34th in line for the English throne. Even though she is penniless, royalty just do not get jobs. Georgine starts a specialized maid service, opening and dusting the London townhouses of the landed gentry before they come up to town. However, Georgine’s only employee is herself. As a maid, invisible to people of the upper classes, Georgine finds herself in awkward positions, overhearing conversations and actually stumbling onto a dead body in this fun mystery.