Buckingham Palace Gardens (Thomas Pitt Mystery, Book 25) - Anne Perry

In the latest compelling book in Anne Perry's bestselling Pitt series, Inspector Thomas Pitt must navigate the upper echelons of society if he is to find a murderer bold enough to kill in Buckingham Palace.
Early one morning, Inspector Thomas Pitt is awoken by a message from his boss, Narraway. A maid has been murdered. The maid worked at Buckingham Palace and Narraway needs his must trusted man to deal with the investigation.
The suspects are narrowed down to a group of guests, meeting with the Prince of Wales to discuss the funding for a huge project: the Cape to Cairo railway. If the murderer isn't found, the Queen will veto royal support for the scheme.
It rests with Pitt to solve the murder - in doing so he must reconcile his own concept of justice with those who feel it is within their right to make their own laws, whatever the consequences.