I will discuss this book on several levels. First, as a mystery, it's not really. I'd say that a large portion of readers will already be familiar with the basic story of the Phantom of the Opera. So, the identity of the "ghost" or Phantom is no secret. And just that fact that there is a real person behind all the mysterious goings-on will be no surprise. Fortunately--on that score--I didn't pick this up at the bookstore and read it because I thought I was getting some dramatically different brain-teasing puzzle. I got it because it was a different spin on the Phantom and on Holmes (more on him later). That being the case, I'll give Sam Siciliano a pass on a rating for the mystery. Those who have never read/seen the original Phantom can better rate the mystery.
Second, if I completely ignore the fact that I am incredibly familiar with the person of Sherlock Holmes as Conan Doyle conceived him, this is a fine story. The story itself is well-written and an exceptionally quick and absorbing read. And I thoroughly approve of the new ending. Replace Holmes with a brand-new detective and I could down-right love this story....Which brings me to the major stumbling block in the book....
This is billed as "The Further Adventures of Sherlock Holmes"--that would seem to me to be a major selling point. Siciliano apparently has great disdain for Holmes as Doyle wrote him. He makes huge changes to the Holmes character and ditches Dr. Watson as the detective's right-hand man. Instead, he gives us Dr. Henry Vernier--Holmes's cousin and best-buddy. The bestest of besties who knows Holmes better than anybody on earth--especially better than that blithering idiot Watson. Vernier is down-right jealous of Watson--that's my only explanation for the character assassination that issues forth from the mouth of Holmes's cousin. And yet Vernier isn't exactly the brightest bulb himself--regularly missing clues and suggestive actions that are as obvious as the nose he holds so high in the air when referring to that other doctor. Listening to Vernier's drivel about how much better he is as a doctor and a friend to Holmes and side-kick was nearly enough to make me stop reading. Take that and the fact that Holmes is suddenly in touch with his feelings (totally understands all this unrequited love business because he had some of that himself) and he's suddenly all about the cash--charging outrageous fees left, right and center--forget the fact that most of his cases he took on because the mystery fascinated him, and...all those references in Doyle that might have made you think Holmes believed in God...yeah, no, Watson was just making stuff up (as he does, you know). Seems to me that this book was just a chance for Siciliano to make the Holmes character in his own image rather than pay homage to Doyle's well-known detective.
So...final summation: Mystery--neutral; Story Itself--very good; Holmes story--pretty darn bad. We'll give it ★★ and 1/2 stars here and round it up on Goodreads.