'It's not enough,' he muttered. He crumpled the paper in both hands and set it aside, then added: 'Poor Ross!'

From this, and from other indications in his behaviour he mentioned, for example, that he might never call upon the services of the Baker Street Irregulars again I gathered that he still blamed himself, in part, for the boy's death, and that the scenes we had witnessed that night on Hamworth Hill had left an indelible mark on his consciousness. n.o.body knew evil like Holmes, but there are some evils that it is better not to know, and he could not enjoy even the rewards of his success without being reminded of the dark places to which it had taken him. I could understand this. I had bad dreams myself. But I had Mary to consider, and a medical practice to run. Holmes found himself trapped in his own particular world, forced to dwell on things he would rather forget.

One evening, after we had taken dinner together, he suddenly announced that he was going out. The snow had not returned, but January was as glacial as December had been, and though I had no desire at all for this late expedition, I nonetheless asked him if he would like me to accompany him.

'No, no, Watson. It's kind of you. But I think I would be better alone.'

'But where are you going at this late hour, Holmes? Let's go back to the fire and enjoy a whisky peg together. Any business you may have can surely wait until the day.'

'Watson, you are the very best of friends and I am aware that I have been poor company. What I need is a little time alone. But we will have breakfast tomorrow and I am sure you will find me in better spirits.'

We did and he was. We spent a pleasant and companionable day visiting the British Museum and lunching at Simpson's, and it was only as we were returning home that I saw in the newspapers a report of the great fire on Hamworth Hill. A building that had once been occupied by a charitable school had been razed to the ground, and apparently the flames had leapt so high into the night sky that they had been visible as far afield as Wembley. I said nothing about it to Holmes and asked no questions. Nor had I remarked that morning that his coat, which had been hanging in its usual place, had carried about it the strong smell of cinders. That evening, Holmes played his Stradivarius for the first time in a while. I listened with pleasure to the soaring tune as we sat together on either side of the hearth.

I hear it still. As I lay down my pen and take to my bed, I am aware of the bow being drawn across the bridge and the music rises into the night sky. It is far away and barely audible but there it is! A pizzicato. Then a tremolo. The style is unmistakable. It is Sherlock Holmes who is playing. It must be. I hope with all my heart that he is playing for me ...

Anthony Horowitz on Writing The House of Silk: Conception, Inspiration and The Ten Rules.

I'm still quite surprised that I was approached to write The House of Silk (I'm a.s.suming, by the way, that you have read it before you reach this point. Spoilers follow!). Although the bulk of my television work is adult, when it comes to fiction I'm better known for children's books in particular the Alex Rider series and I'm fairly sure that the Doyle estate wasn't interested in a fast-paced action thriller full of explosions and improbable chases. They'd already had plenty of that with Robert Downey Jnr. At the time, they weren't even aware that I have long been an admirer of the Sherlock Holmes novels and short stories. I was actually given a set by my father for my seventeenth birthday (I think) and they immediately wove themselves into the fabric of my life. I cannot now read The Dying Detective or The Devil's Foot (two of my favourites) without somehow regressing into my teens. For me, Jeremy Brett was the finest TV Holmes and watching occasional re-runs on ITV3, I find myself being taken back to my late twenties and can see the house where I lived, even the clothes I was wearing. There are very few characters in fiction who have the power to do this but Holmes is certainly one of them.

It may well be that Sherlock Holmes is the reason why I have spent so much of my life writing crime fiction of my own and if there is one small boast that I occasionally make, it's that I have probably written more fictional murders than any other writer. Ever. The crime figures can be quickly totted up.

I helped to create Midsomer Murders from the novels of Caroline Grahame ('Agatha Christie on acid') and they certainly have the highest body count on British Television. I wrote the first seven episodes which saw no fewer than nineteen fatalities including Elizabeth Spriggs (poisoned), Anna Ma.s.sey (pushed out of a window) and Orlando Bloom (stabbed with a pitchfork). In the early days of MM, writers were encouraged to develop a bad habit in that whenever an advertising break approached, someone would be killed simply to make the story more interesting and to encourage the audience to keep watching. It could be argued that in the end this would turn the series into a parody of itself. For my part, I had to give up writing the show when I realised that there was hardly anybody left in Midsomer to murder.

Before MM, I adapted fourteen hours of Agatha Christie's Poirot, which averaged at least one murder in the short stories, often two or three in the novels. A less successful original series of mine, Crime Traveller, had a detective travelling back in time to prevent murders and invariably feeling (it was a time paradox ... if there hadn't been a murder he would never have travelled back in time so the very fact that he had done so proved that it had to have happened). Eight hours, eight more deaths. Given that they were supposed to be a slice of UK life in the 21st Century, there were a surprising number of murders in the two five-part shows that I developed for ITV: Collision and Injustice.

And then there's Foyle's War, which has now run for ten years on ITV with Michael Kitchen superb as a reluctant detective investigating crimes during the Second World War. Perhaps this was the programme that brought me to the attention of the Doyle estate. More serious and low-key than Midsomer Murders, it was set in the past, very carefully researched and perhaps more in keeping with the book they had in mind. I wrote twenty-one two hour episodes and although we did our best to keep the body count down (my favourite episode, The French Drop, has no murder at all) the deaths still added up.

And that's not counting my children's books. The Alex Rider world is necessarily a violent one. I have produced over thirty horror stories. And then there are the less well known but surprisingly blood-splattered detective stories featuring the Diamond brothers. I Know What You Did Last Wednesday, contains seven violent deaths in just seventy-eight pages.

I'm often asked why readers have such a keen interest in murder. The short answer is that actually I think we don't but in fiction, whether it's television or books murder is a simple, very immediate way of focusing attention on a character. We may have no particular interest in a man who makes pizzas but the moment his wife is found with her head in the pizza oven, we're forced to ask questions about him, to look behind their relationship, to search for the truth. In detective drama, the viewer and the detective have a very similar role. And what is it about the British that makes us so pre-eminent in this field? Well, I think the fict.i.tious county of Midsomer provides part of the answer. As a race we're very secretive. By and large we don't display our emotions in the same way as, say, the Americans. We live behind net curtains. This is an atmosphere very conducive to murder and it reminds me that when I put together a doc.u.ment to explain the ethos of Midsomer Murders this was before the series had even been commissioned I put at the head of it a famous quotation from the Sherlock Holmes story, The Adventure of the Copper Beeches: 'the lowest and vilest alleys in London do not present a more dreadful record of sin than does the smiling and beautiful countryside.'

How do I set about creating a murder mystery? This is another question that often comes up at literary festivals. For me, all murder stories boil down to a very simple formula: A+B=C. A is one person. B is another person. C is the reason why A wants to murder B. The genius of Agatha Christie was that she managed to find so many variations on this basic formula. The narrator did it. The detective did it. The little boy did it. They all did it. And yet, the strange thing is that when you come to think them up, there are very, very few reasons why anybody actually wants to murder anybody. In fact I can only really think of three: money, fear and pa.s.sion ... which may be s.e.xual pa.s.sion, revenge or whatever.

I see a murder story as a series of concentric circles, almost like a dart board. At the very centre is that equation. It is where I start because it is both the beginning and the end; the springboard and the solution to the crime. But then I have to add the next levels. The other suspects. More stories which, though often irrelevant, nonetheless link up with the bull's eye. In Foyle's War, I would add whole stories which had nothing whatsoever to do with the crime but which in many ways interested me much more: anti-Semitism in Britain, the birth of plastic surgery, funk holes, spies, etc These would all be layered in. Every book has to have a shape. A murder story is circular.

If there was a model for Foyle or, for that matter, Midsomer Murders, it was probably closer to Agatha Christie or Dorothy L. Sayers than Doyle. The crime is committed. The detective is introduced and pursues a scattering of clues, meeting people who all add a new perspective to the original crime. A second murder takes place and seems to send the story in a completely new direction. At last the suspects gather in one place. The detective has his moment in the spotlight and if he's Poirot he accuses everyone in the room before he finally settles on the guilty party who is, of course, the last person you expected. The guilty party claims innocence. Cue the flashback. Poirot is proved right. Everyone goes home.

All of which is actually completely irrelevant to Sherlock Holmes because Doyle's approach was completely different. Take, for example, the twelve stories which make up the collection with the t.i.tle The Adventures of Sherlock Holmes. No fewer than nine of these contain no murder. Even more remarkably, three of the stories A Case of Ident.i.ty, The n.o.ble Bachelor and The Twisted Lip don't even contain a crime. Throughout the canon, there is a remarkable shortage of red herrings and suspects. One of the two favourite stories that I mentioned, The Dying Detective, is virtually a two-hander. In one story, the killer is a horse. In another, it's a jellyfish. Even more oddly, if you look at the four novels, three of them A Study in Scarlet, The Valley of Fear and to a lesser extent The Hound of the Baskervilles even manage to lose sight of the detective, transporting us to Utah, to Vermissa and to Dartmoor.

If you were to ask what has made Sherlock Holmes the most successful and best loved detective of all time, I would argue that it is not in fact the crimes or the mysteries. It seems to me that the appeal of the books has much more to do with character, the friendship of Holmes and Watson, the extraordinary and very rich world they inhabit and the genuine and often under-rated excellence of Conan Doyle's writing, a touch melodramatic at times but still very much in the tradition of gothic romance. When I was asked to write The House of Silk, I realised that this would be the key. I had to become invisible. I had to find that extraordinary, authentic voice.

And the first two challenges were immediately apparent. The first one was the length. My publishers, Orion Books, had requested a novel of between 90,000 and 100,000 words (the final length was around 94,000) big enough to seem like value for money on an airport stand. But actually, this goes quite against the spirit of Doyle's originals which barely run to half that length. The very nature of a Sherlock Holmes story is that the narrative has a slightly silky feel. The chapters are short and to the point. Characters are not described at any great length and even Victorian London is economically sketched in. Nor are there any major action sequences as such. A boat chase down the River Thames, yes. A midnight encounter with a h.e.l.l hound on the moors. But these are singular occurrences. The greater part of the novels take place in closed rooms ... hardly ideal for a modern audience and certainly of no interest to any circling Hollywood producers (well, it's just a thought).

The other challenge was the t.i.tle. Modern novels, particularly the sort of bestseller than Orion had in mind, have to shout loud on a crowded shelf. Doyle, although he had an uncanny eye for what the market wanted, was less troubled by such commercial pressures. The Sign of Four is a perfect t.i.tle and many of the short stories have the same gentle elegance: The Problem of Thor Bridge or The Golden Pince-nez. Although t.i.tles for the Alex Rider books were always a bit of a struggle, I decided on The House of Silk at a very early stage. It just felt right.

I should also add that the plot of the book came very quickly. In fact, by the end of my original meeting, when I hadn't even accepted the commission, most of it was in place. This is very rare for me and helped persuade me that I should go ahead. Writing the book was also an intense pleasure and I hope I won't sound arrogant when I say that I think it is my best work. I am not superst.i.tious by nature but Doyle, of course, was a confirmed spiritualist and before I began writing The House of Silk, I went out and bought an old Holmes edition which he had personally signed. It was with me the whole time and that tiny, neat signature became something of a talisman for me. I even felt occasionally (or was tempted to feel) that Doyle was in some way watching over me, guiding my hand. This may sound completely ridiculous but it's just how it was.

By a strange coincidence, I was invited to give a talk to the Sherlock Holmes society in the House of Commons while I was writing the book and it was then December 2010 that I announced it for the first time. I can't say they were completely overwhelmed. These people take Holmes very seriously. They can recognise a short story from a quotation of three or four words. Once a year they visit the Reichenbach Falls and dress up as their favourite characters. They are not eccentrics or fanatics but they are fairly extreme and they can be found all over the world.

This essay is, in part, adapted from the talk I gave that night. And it seemed important to me to rea.s.sure them that I was not going to play fast and loose with their beloved creation. Part of this was commercial good sense. If you annoy the core enthusiasts, you're going to make enemies you don't need. I have had contact with several estates Tintin, Agatha Christie, Ian Fleming and know this to be true. But I was more swayed by a sense of personal responsibility. I liked Sherlock Holmes much too much to want to muck him up.

And so I set out the ten rules which I would have beside me as I wrote The House of Silk and here they are again. If you've read the book, you can judge for yourself how well they were kept and, indeed, if they were worth keeping.

1. No over-the-top action. I've already touched on this but after writing nine Alex Rider novels, this was the most difficult, the most exasperating piece of self-restraint. It's difficult to think of a modern thriller without gun-fights and car chases. We all know that Holmes is an expert singlestick player, boxer and swordsman and occasionally carries a firearm. But the original stories have a cerebral, even sedentary feel to them. My image of Holmes is in his study, in front of the fire not escaping from circular saws or diving six storeys into the River Thames. All that I can leave to Robert Downey Jnr. The House of Silk has disguises. There are expeditions to Bluegate Fields, to Vauxhall and to the slums of Boston ... but I hope I have managed to avoid the genre-crossing extremes which, though enjoyable, might best be described as Indiana Holmes. I have to admit, though, that I was quite pleased to be able to sneak in the brief coach chase at the end.

2. No women. Of course it was tempting to create a romantic lead, to give Holmes a love interest. But re-reading the short stories before I began work, I came almost immediately upon that famous sentence 'To Sherlock Holmes she is always the woman' and knew at once that it would have been madness to try and create another Irene Adler. I did briefly think of bringing Irene back (I believe she appears in the second Holmes movie) but I felt somehow it would have been taking a liberty and anyway Watson had already set the seal on that subject: 'All emotions and that one (love) particularly, were abhorrent to his cold, precise but admirably balanced mind.'

3. This is very much related to rule number two. There would be no gay references either overt or implied in the relationship between Holmes and Watson. This was hinted at in Billy Wilder's film, The Private Life of Sherlock Holmes which has a scene with Watson tangled up with dancers from the Bolshoi ballet. But it is of course silly and wrong although I did have an advantage, being a modern writer, in that I was able to examine some aspects of the s.e.xual mores of Victorian England in a way that Doyle could not.

4. No walk-on appearances by famous people. The American writer, Nicholas Meyer put Holmes together with Freud in his 1974 novel, The Seven Percent Solution. Billy Wilder had Queen Victoria. I've heard that one Doyle pastiche even has Holmes meeting Hitler! But for me the power of the books is that they largely create a world of their own with very little reference to contemporary affairs. Holmes quotes Goethe, Flaubert, Petrarch, Poe and Winwood Reade but even his most august clients The King of Scandinavia or Wilhelm Gottsreich Sigismond von Ormstein, the Grand Duke of Ca.s.sel-Felstein tend to be fict.i.tious. This seemed to me to be a good rule so I followed it too.

5. No drugs at least, none to be taken by Sherlock Holmes. Although Holmes now has a reputation for being something of a cocaine fiend, it's only in The Sign of Four that we meet him when he is actually taking the drug. I was very nervous of doing any post-modern take on Holmes and it struck me that to have him ravaged by cocaine would only detract from the story-telling. I knew that drugs would play a part in the story I wanted to describe an opium den because Holmes had never actually visited one but drug addiction was out.

6. Do the research. Try to get the details right. It's unlikely that the Doyle estate knew this or cared but all my life I have read and enjoyed nineteenth century literature: d.i.c.kens, George Gissing, Anthony Trollope, George Meredith and so on. This made writing the book and finding my voice a lot easier. I also received a great deal of help from other sources you'll find them in the acknowledgements page. That said, I'm sure there are plenty of mistakes too ... and will argue (when the time comes) that this is entirely in the spirit of Doyle who was himself occasionally slapdash. Watson's wound, for example, moves from his arm to his leg. And most famously, in The Speckled Band, snakes cannot climb ropes!

7. Use the right language. It's quite difficult to pastiche nineteenth century English in a way that won't put off twenty-first century readers, particularly younger ones. I have to say that I plucked quite a few words out of the original stories to act as guideposts, to give the text a sense of authenticity. My favourites are: 'snibbed', 'foeman', 'sickish' (used by Lestrade) and 'pa.s.s.e.m.e.nterie'. That said, the book is actually being written in around 1916 and I would imagine that by this time Watson's own language and writing style would have become more modern.

8. Not too many murders. Again, this is a point that I've already made but it was a very important discipline to set out at the start. And actually, when I count up the bodies, it does rather looks as if I've failed.

9. Include all the best-known characters but try and do so in a way that will surprise. Mrs Hudson is there, of course, as well as Lestrade, Mycroft and Wiggins. In each case, I added very little to what was known about them simply because it seemed to be taking liberties. I have, however, given Lestrade a Christian name ... Doyle only every provided an initial. And of course, I had to have Moriarty in the book ... that was obvious from the start. Even so, I shied away from making him the main villain. It's odd that a character who is only mentioned in about three of the Sherlock Holmes stories and who only appears in one should have had such a huge impact on crime fiction. Perhaps it has something to do with his name? I loved including him in Chapter 14 and although I have no plans to write a second Sherlock Holmes novel, I have a suspicion that the two of us will meet again ...

10. Rule number ten was the most important rule of all and as I am writing this in August, before the publication of The House of Silk, I don't yet know if Orion will have twisted my arm and made me break it (the rule, not my arm). It was this. When publicising the book, never, ever be seen wearing a deerstalker hat or smoking a pipe. I actually asked my agent to put this into the contract.

By the time you read this, I will know if The House of Silk has been a success or not. All I can say is that I have never written a book with more pleasure nor been more pleased with the result. This essay appears, I believe, in the ebook. Doyle, who was always a man ahead of his time, would have had no trouble with it but personally I find it hard to believe. No paper, no cover, no back cover blurb? But then I always was old-fashioned. The nineteenth century is where I most like to be.

Anthony Horowitz.

August, 2011, Crete.

Ten Fiendishly Difficult Questions about Sherlock Holmes.

1. Who wrote 'Dynamics of an Asteroid'?

2. What was Victor Hatherley's profession and which part of his body did he lose?

3. What do the killers in The Speckled Band, The Lion's Mane and Silver Blaze all have in common?

4. What was Mary Watson's maiden name?

5. What links The Greek Interpreter, The Final Problem, The Empty House and The Bruce-Partington Plans?

6. Why is The Adventure of the Mazarin Stone unique?

7. Napoleons plus students plus gables plus orange pips equals what?

8. What relevance does the answer to Question Seven have to 221B Baker Street?

9. Who was 'the second most dangerous man in London'?

10. Name the odd one out: Inspector Lestrade, Wiggins, Dr Watson, Mrs Hudson.

ANSWERS.

1. Professor Moriarty.

2. He was an engineer. He lost his thumb. (The Engineer's Thumb) 3. They were all animals.

4. Mary Morstan.

5. Stories in which Mycroft Holmes appears or gets a mention.

6. It's the only Holmes story told in the third person.

7. 17. (The Six Napoleons, The Three Students, The Three Gables, The Five Orange Pips).

8. There were seventeen steps to Holmes's rooms.

9. Colonel Sebastian Moran (The Empty House).

10. Dr John Watson. The others have no Christian names.

end.