This book is written so closely to the style of Sir ArthurConan-Doyle that I hope the author will mull over the idea of writinga Sherlock Holmes book.
The "voice" of the novel is dead on. It reads very much like Doyle's writing, which helps keep the reader immersed in the time period of the story.
Finally we get to learn more of Sherlock's brother, lesser known but more important to England, Her Majesty, and the Admiralty.
The intrigue surrounding the treaty with Japan could have actually taken place, if in fact it did not. Quinn Fawcett certainly did his homework concerning the political events and who would gain or lose depending on the fate of the secret treaty.
Compare this excellent book with the writing of some of the modern Sherlock Holmes stories, like "The Ice Palace Murders" or "The Haunting of Torre Abbey". After seeing Holmes and Watson grafted and mis-cast into standard or sub-par mystery stories at the hands of modern writers, "Embassy Row" was a rare treat.
While Mycroft's game is more of espionage and intrigue than the "trifles" of Sherlock and his deductive detecting, Mycroft's brilliance is clearly shown, as are the reasons for his importance to the government of England.
Guthrie is an interesting character, somewhat Watson-like. He takes on the role of narrator as well as confidential secretary. The author has chosen well to keep the Mycroft series somewhat like the Sherlock Holmes canon in style and tone, but this has not stifled his ability to create something very new and entertaining.
This is a wonderful series, and I hope the author will one day favor us with some stories of the better-known brother who resides at 221b Baker Street. He certainly has the "voice" to make a Sherlock Holmes story quite memorable.