I read reviews warning the reader to skip over this one in the series, but that advice goes against my nature as a reader.
I wish I had been able to listen.
Meanwhile, the book is summed up as follows. (Here be spoilers)
Holmes--"Russell, come to rainy, foggy Devonshire."
Mary---"No." (Changes mind)
Mary tramps through mud, gets wet, dirty, hungry cold. Takes bath.
The Reverend Baring-Gould, "I won't be around much, but I am old, my house is queer, and I don't think much of you, only Holmes."
Mary, "Likewise, I'm sure."
Mary tramps through mud, gets wet, dirty, hungry cold. Takes bath.
Repeat.
Mary and Holmes learn nothing, but remain in Devonshire.
Holmes, "I know I sent for you in a great hurry, but now I'm going to London. Will you tramp through the mud some more, learning nothing?"
Mary, "Certainly not!"
Holmes, "Russell, I'll be back in 50 pages or so."
Mary, "That usually means a hundred at least. Holmes, that's 1/3 the book!"
Holmes, "Can't be helped. This series is about you."
Mary, "Tramping endlessly through the mud and taking baths is not improving my character."
Holmes, "Sorry. Must be off."
Mary tramps through mud, gets wet, dirty, hungry cold. Takes bath.
Repeat.
Holmes, "I'm back from London. Learned nothing there, really. You?"
Mary, "No! Oh for heaven's sake Holmes, haven't you learned yet that we only solve mysteries together?"
And they wrap it up.
Just skip this one. "O Jerusalem" is far better, and does make up for many of the sins of this book.