I was never going to completely warm to this story simply by virtue of the fact that it violates one of my two golden rules. The rule in question being that Sherlock Holmes pastiches should stay firmly within the world of Holmes and this one strays into Phantom of the Opera territory. However, in the interests of objectivity, I shall put that temporarily to one side.
The biggest challenge when writing a pastiche is that of mimicking the original author's style. When you have a cross-over you have the problem of balancing two (or possibly more) styles. In Workman's case she is juggling three - Conan Doyle, Leroux and Lloyd Webber. Inevitably one of these influences has to dominate the book and I personally believe that Lloyd Webber is the winner here with the result that Holmes and Watson don't speak as authentically as they should. To be fair, no Holmes pastiche I have ever read has truly managed to capture the spirit of Conan Doyle but I have read many that have come closer.
Another problem comes from trying to step into the heads of too many of the characters (which is another significant departure from the style of most Sherlock Holmes stories). Sections are written from the perspective of Watson, Holmes and Raoul which is, I think, two too many. Also it is not always immediately clear with each chapter whose head you are occupying.
Next I come to matters of editing. I appreciate that the author is American but if you are writing a Holmes pastiche from the perspective of characters from Victorian England they must be both Victorian and English. Workman, at the beginning of the story, describes Holmes being shot in the leg. Writing as Watson she uses the word 'pants'. This is simply unforgivable. As an Englishman, Watson would say 'trousers' and nothing else. It would be perfectly acceptable for an American character to use the term but not good old Watson.
I would advise the author to make sure she has an editor fully conversant with English English on board for her next effort in order to weed out such little oversights.
All the above said, the book flows well and never seems to drag. The only part which really didn't ring true for me was the sword fight between Holmes and the Phantom. However I suspect this stems from the fact that I have experience of fencing - something which I suspect the majority of readers will not have and will therefore not be troubled by.
In short the basic problem with this story is that it is attempting to be a Holmes pastiche featuring the Phantom of the Opera but ends up being a Lloyd Webber inspired Phantom pastiche that features Holmes and Watson. If you understand this at the start I think you will enjoy the book more. If you start it expecting a Holmes adventure I think you will be slightly let down.
If Kate Workman tackles some of the obvious issues I think her next book will be something I shall definitely check out.