I've seen the series touted as an homage to the golden age of British detective fiction, and while it's certainly set in the interwar period in England, it didn't necessarily feel like it was of the period to me. It's very well crafted, with the hallmarks of the era (courtroom drama, skullduggery, genteel (and not so genteel) murder, suspects gathered together in a gloomy stately home), but the setting could have been any time from about 1920 to the present day (except for the capital punishment parts).
The plotting is rather slow, built up over time rather than explosive. The narrative arc is deliberate - stately even, and the denouement is less of a crescendo than an inescapable inevitability when it finally comes. There were a number of fairly outlandish plot twists which interfered with my suspension of disbelief, but in the end the plot threads resolve, the clues are deciphered, and the mysteries are solved.
There is very little background information provided by the author, so the book (in my opinion) doesn't work very well as a standalone. I do recommend the series and the author, so reading the first volume will reward diligent readers.
Four stars. Not classic golden age, but quite readable (and edgy with a sort of noir vibe).
Disclosure: I received an ARC at no cost from the author/publisher for review purposes.