So: does Moriarty exist, or not? Well no, not really, and not just in the literal sense of being a fictional character. He’s hardly even that. We have no evidence beyond Sherlock Holmes’s word, and if you look at Holmes’s behaviour in ‘The Final Problem’ you can see an almost classic case of paranoia — brought on, no doubt, by a heavy cocaine binge. Michael Dibdin, in his The Last Sherlock Holmes Story, therefore proposes that Holmes and Moriarty are the same person, which does redeem Holmes’s otherwise hasty and implausible dispatch by his creator over the Reichenbach Falls.
Anyway, he appears here, in the same year (as far as I can tell) as the events described in The Final Problem; but the meeting is with Dr Watson, so we know it must be true. Or ‘true’. Kidnapped by one of Moriarty’s minions, Watson is brought face to face with the Napoleon of Crime:
‘I have often wanted to meet you, Dr Watson,’ my host began. ‘It may surprise you to learn that I am a great admirer of yours and have every one of your chronicles.’
Actually, this comes as no surprise at all. (Only Holmes is mean about Watson’s writing, so Doyle can express his self-disgust.) Although it is a bit of a surprise to learn that what Moriarty wants to do is help spring Holmes out of jail, and bring down the secret and very bad society the House of Silk, the nature of whose crimes is so vile that Watson has instructed that his story should remain unread for 100 years (we jump the gun here a bit, as he writes during the Great War). Unlike that of the Giant Rat of Sumatra, this is a story for which the world is finally prepared.
We know what we want from a non-canonical addition to the Holmes corpus. We don’t want any fancy stuff, Holmes being Moriarty or a baddie or similar. (Although the Dibdin book is actually very good.) We want Watson to be almost pathetically loyal, but with his trusty revolver in his pocket, we want the Baker Street Irregulars, Lestrade, Mycroft, pea-soupers, sinister foreigners, grotesque crimes, opium dens, and above all, we want Holmes being himself: the only intellectual this country has ever taken to its bosom. We want the atmosphere. We also do not want him to do anything like fall in love, and we do not want the prose to be anything that would sound out of place in the Cornhill Magazine.
Horowitz, despite having a rather suspicious sounding foreign name (and being the very successful author of, among other things, the Alex Rider series of adventure books for children), does a thoroughly first-rate job, cramming all the above desired elements in and just steering clear of making the novel look over-stuffed; although one huge clue was so easy to spot that I wondered whether it was deliberately so, or whether decades of reading Holmes stories had sharpened my eye. Whether one will want to re-read the book in a few years’ time, as one does with the originals, is another matter.