I don't usually see the movie first and read the book later; most of the time, it's the other way around. However, I saw "Mr. Holmes" and decided that I had to read the book -- and, for a change, I'm glad I did it in that order. The changes between film and text are fairly significant.
In this book, Sherlock Holmes is 93 years old and living in a little Sussex home and keeping his beloved bees. His housekeeper, Mrs. Munro, is the latest in a long series of suffering women, and her son Roger is fascinated by Holmes and his bees alike.
Holmes is very well aware that he is losing his faculties, which makes this book a sometimes disheartening read. However, while he is still able to remember things, he is writing the story of his last case. He is also haunted by memories of a visit to Japan, so there is a third subplot involving that.
This is a tightly composed book, with a contrapuntal design that keeps the flow of each story without being disruptive in any way. The author gives us a more rounded Holmes than Doyle did, letting us into the aging detective's inner life.
I enjoyed the book very much and would recommend it highly.