"The Canary Trainer" by Nicholas Meyer

For years, I have wanted to read a book that inserts Sherlock Holmes into The Phantom of the Opera  by Gaston Leroux.  Why?  Because the edition of that book I first read, way back in 1999, mentioned that some people suggest that the "Rat Catcher" character might actually be Sherlock Holmes in disguise.  I have since learned that Leroux was actually a HUGE fan of Sherlock Holmes, and it's very possible that he meant the Rat Catcher to be Holmes in disguise.  

Well, what Holmesian wouldn't want to ...