Music has frequently been a catalyst for me in the creating of a plot, and it seems to have found its way into a good many of my books. There’s the eerie death lament, ‘Thaisa’s Song’ in The Bell Tower, and the music hall songs in Ghost Song. More 
recently, there’s the Phineas Fox series, with a music historian and researcher as the central character – although it has to be said that while Phin certainly gets entangled in music mysteries, he also finds himself drawn into other intriguing situations
But one of the difficulties with using music as a frame for a plot, is the embarrassment of riches that music’s history offers. There’s the macabre – such as the legend of how Paganini’s body was refused burial because of alleged participation in satanic rituals, and was apparently trundled across Europe for the best part of four years, before an appeal to the Pope finally allowed conventional burial. That practically presents itself as a complete plot, there for the writing. Or, if an author happens to incline towards the realms of the supernatural, there’s the dark tale of 
the Piper of Hameln to draw on – that infamous figure from the Middle Ages, who, when the townspeople reneged on payment for his rat-catching services, wrought his grisly revenge by luring the children into the mountains by his magical music. You do have to be wary of sinister strangers offering peculiar deals, although the legend has certainly provided material for such diverse names as the Brothers Grimm, Robert Browning, and Walt Disney.
And, staying with the supernatural, might there really be a ‘Curse of the Ninth Symphony’, given that a surprising number of composers died after completing their ninth? The composer Philip Glass was convinced of it – to the extent that he insisted on completing his tenth symphony before allowing his ninth to be performed in public.
Moving away from the macabre, there’s the humorous, such as the Elizabethan 
caperings of one Will Kemp. Master Kemp was a Shakespearean comic actor and ‘purveyor of mad jests and merry jigs’, and he accepted a bet that he could not dance from London to Norwich – roughly 80 miles (132 km). He won the bet, although it took him nine days to do it – which he later chronicled as ‘The Nine Daie’s Wonder’ [sic]. Happily, though, the nine days don’t seem to have been entirely without a few lighter moments; one version tells how, at one part of his journey, a young lady came out and danced a mile with him, to keep him company. Some versions suggest slyly that caperings of a different kind took place, as well. But that would be a tale for an entirely different kind of book, and in any case, Shakespeare, if he heard about his actor’s exploits, would have instantly spotted the potential for a bawdy romp scene, and very likely used a version of it in several of the plays. (He probably did just that, although probably not in Hamlet or King Lear).
There are other, more straightforward mysteries, of course. There’s a definite whodunnit flavour in the question of whether Salieri really did murder Mozart – witness Peter Shaffer’s play/film ‘Amadeus’, and also Alexander Pushkin’s 1830’s poetic drama, ‘Mozart and Salieri’. There’s the question of why Schubert never finished his ‘Unfinished Symphony’. To come more up-to-date, there’s surely a lively quest to be mapped out in solving the meanings and identifying the characters in Don McLean’s ‘American Pie’.
And so Phineas Fox, in his second outing, might have found himself imbroiled in any one of half a dozen plots, ancient or modern, classical or rock or jazz, any of which could be based on true stories. I considered and discarded and researched and re-considered. I tumbled half-forgotten books from my shelves, dispossessing armies of indignant spiders in the process, and I trawled libraries and the internet.
Then I latched onto the infamous tritone – the ‘Devil’s Chord’.
If we’re going to be technical (which always sounds nicely scholarly and looks impressive in this kind of article), the devil’s chord is an augumented 4th, or Tritonus, and spans three steps in the scale. It’s been described as one of the most dissonant music intervals around – so much so, that it was banned in Renaissance church music. Church music was supposed to be a paeon of praise to God, and the tritone was considered so ugly that it wasn’t thought suitable. Medieval arrangements even used it to represent the devil, and Roman Catholic composers sometimes used it for referencing the act of the crucifixion. Its dissonance can work to advantage in some cases, though. It’s remarkably effective as background music in films, where it can serve as a warning to the audience that something bad’s about to happen. That harsh discordance that tells you the killer’s outside the door with an axe. Think shower curtains in Psycho.
It occurred to me that the devil’s chord might make a guest appearance in a composition that had become part of music legend. But what could that legend be?
Well, as somebody once said, if you can’t find a genuine legend, create one of your own.
Music has often been composed to celebrate great events – coronations, births, victory in war. But what about a legend in which a piece of music was written to celebrate not a happy, or a triumphant event, but something far darker? Something so menacing its existence was kept secret?
It was at that point that I saw the whole plot. I could see Phineas Fox peeling back the layers of a secret that had lain undisturbed for three quarters of a century – glimpsing edges and corners of it, and ending in delving into a very grisly fragment of musical history indeed.
And so, Chord of Evil was born.
Source: Sarah Rayne Blog