I greatly enjoy Anne Perry's Thomas and Charlotte Pitt mysteries. Historical mysteries are tricky, requiring one to not only be well versed in the period in which the story is set, but the judicial system and detection methods available at the time. While I can't attest to how accurate Perry is in her facts, she maintains a willing suspense of disbelief.
In Buckingham Palace Gardens, someone commits a murder at the eponymous royal palace. The Queen isn't in residence, but the Prince of Wales is. Four men are implicated; they are staying at the palace to discuss the construction of a massive railway from Cape Town to Cairo. Thomas Pitt takes the case (much to his regret, I'm sure).
From a shortlist of suspects, Perry manages to weave both suspense and doubt throughout the story. Although much of the mystery is predictable, she includes a final twist that isn't immediately apparent even if you deduce the culprit. I figured it out slightly before the reveal, but it was still nice to see Pitt stand up to the Prince of Wales (who is his "better" in that era) in the name of justice.
I loved the involvement of Gracie in the investigation! Watching her interact with the palace staff was hilarious. Of course, she proves indispensable to the investigation; Pitt would never have solved the mystery without her assistance. Yet she remains modest and probably awed at her contribution to what was, in the end, a matter of the state and a matter of treason. Gracie grows as a character during this novel. The events affect her perspective regarding her upcoming marriage to Sergeant Tellman, as well as how she perceives her unusual (for the serving class) ability to read, which endears her to one of the suspects.
Parts of the story could be confusing. The character of Cahoon Dunkeld, a blustery bully, was larger-than-life; I didn't like it at all. Likewise, the Prince of Wales seems rather two-dimensional. In the case of the latter character, I suspect Perry did this intentionally to demonstrate the gulf between the lower-middle class, like Pitt, and royalty. Had there not been a murder, Pitt would never have been in the palace. Considering the circumstances, I suppose I can suspend my disbelief in that matter.
I don't remember the last Pitt mystery I read, so I can't compare Buckingham Palace Gardens to Perry's other work. I consider it a good read--nothing amazing, but certainly a good mystery novel.