Man, I really liked this one. It ticks a lot of my pastiche boxes; most especially, that it's set in 1919 (putting it firmly in "His Last Bow" territory, which always delights me). Not enough has been written of Holmes and Watson's adventures in the era of WWI and after, perhaps because Conan Doyle established that Holmes retires and moved to Sussex at the end of his detecting career. But of course, for Holmes, detecting is a calling, not just a profession; and Conan Doyle himself wrote a couple of stories about the Great Detective following the threads of a mystery even after Holmes's retirement. Pastiches featuring an older Holmes and Watson are favorites of mine, and I was thrilled to find one as enjoyable as this.
While there is, as others have noted, a definite sense of science fiction to this read (especially towards the end), this book is a true adventure novel. I don't mean to knock the mystery of the book -- because there is so clearly a mystery, and an engaging one at that -- but there's a lot of chasing and confronting and perilous escapes; it is, indeed, an _adventure_.
That's not to say we don't have plenty of time for character development. I loved watching Watson struggle to decide how much Holmes was still a part of his life, and how much he wanted him to be; I loved watching Holmes struggle to reconcile the known with the unknowable. (Damn, those last two paragraph are crackerjack; I can't remember the last time an ending line so pleased me.) These are real people here, real _friends_, and I loved seeing that friendship so wonderfully displayed.
One especial note: I get frustrated with pastiches and adaptations that portray Sherlock Holmes as flawless. It drives me particularly batty when a story will have Holmes getting physically injured or emotionally bested, only to have him turn around in a few scenes and go, "Oh, ha ha, I wasn't hurt/debilitated/in danger at all! That was all an act, a disguise! It actually fit into my plan all along!! I was in complete control of the situation the whole time!" People seem to forget that Conan Doyle had the Great Detective fail on several notable occasions, and it doesn't seem to occur to writers that having a faultless character who is always two steps ahead of the villain makes for less-than-dramatic reading. How can there be any tension, or indeed any real triumph, if Holmes is always in complete, superhuman control of all aspects of the situation? So I really appreciated Scott's balance here: when Holmes got hurt, he was _hurt_, and if he was still able to rally to continue pursuing the case, it did not undo the stakes because, y'know, the _stakes actually existed_. (This, of course, makes it MORE impressive when Holmes wins the day, because he's doing so against stacked odds. When your hero is in perfect control of every detail the entire time, it's much less impressive, and I appreciate that Scott _got_ that.)
I recommend this one especially to fans of the Downey-and-Law Holmes & Watson duo, because the banter between Scott's Holmes and Watson put me so in mind of the sibling-like friendship between Downey and Law's takes on the characters. I hope this isn't the last Holmesian pastiche from Mr. Scott.