I have the sneaky feeling that this book was written tongue-in-cheek. Having Sherlock Holmes summoned from England by the Emperor of Brazil to come to his country and solve the mystery of the theft of a valuable violin far exceeds the imagination stretching required in this situation. Also, making Watson the complete bumbler (just as Nigel Bruce played him in the Basil Rathbone movies) does real damage to his image, and is really not in conformance with his character as set out in the novels and stories.
Also, we have Sherlock falling in love and acting like a smitten schoolboy, which is so far from his character that it's almost ridiculous! All of that having been said, the book was somewhat fun to read and I learned a lot of Brazilian history. If you aren't a Holmes stickler you might enjoy this book; if you are, stay as far away from it as possilbe!