By the end of the book the mix works very well, with a lot that has been left hanging from the previous two novels resolved - but along the way it was decidedly hard work. This is because most of the main characters are, for various reasons, miserable and suffering throughout the book. Although this certainly gives the characters challenges to face, it can result in rather dour reading material.
As Buffy the Vampire Slayer proved so well, by far the best way to deal with the apparently impossible challenge of integrating the fantastical and the everyday is through humour. And humour was behind a lot of the resilience of the characters and interest in the plot in the first book. But here, things are so bleak for so long that is hard to really enjoy the book until you make it to the last few chapters.
Even so, the resolution is well handled - and there is clearly a lot more to mine here, if Cornell chooses to do so. He has moved an interesting character from the sidelines into the spotlight, which bodes well for future books. As long as Cornell can keep the mood a little more variable in future titles, rather than keeping things so uniformly bleak, we can look back on Who Killed Sherlock Holmes as a necessary low point to work through and get on with enjoying the rest of what is still one of the best urban fantasy series of the moment.
Who Killed Sherlock Holmes is available from amazon.co.uk and amazon.com.