When I began to write the first of the Michael Flint/Nell West haunted house series, I didn’t actually know it was destined to become a series. In fact I had never previously considered writing a series at all – or even so much as a trilogy.
Despite working in the kind of muddle 
with which Sherlock Holmes might have sympathised, (‘Don’t disturb the dust, Watson, the varying layers are my filing system,’) a kind of symmetric romanticism always took over when I approached the ending of a book. Having inflicted shattering events on the protagonists, ranging from long-reaching tragedies on the Greek scale to mere murder, I could never bear the hero and heroine to miss out on their hand-in-hand into-the-sunset moment. Even the villain might enjoy the occasional bright interlude before being summarily banished to his or her fate. Life shouldn’t be all 
gloom and misery, even for multiple murderers. This compulsion to provide a neat, happy finale was so strong I often had to be restrained from painting impossibly sentimental word-pictures of moonlit terraces or technicolour skies, and if I could somehow import the strains of Rachmaninov’s 2nd Piano Concerto into the closing paragraphs I usually did.
But once you’ve written that emotional, emotive closing scene, where can your characters go 
next? Do you keep them happily together, letting cosy domesticity into the plots, so that they solve murders while shopping or washing up, or disinter ancient secrets inbetween choosing new bedroom curtains and worrying about the central heating boiler? Or do you scrub the sunset finale altogether, and let them lurch on their own, book by book, from one love affair to the next?
Then I wrote Property of a Lady, and almost without noticing it, a series was born. Because when I finished that book, I saw that my Oxford don, Michael Flint, couldn’t possibly be banished to the obscurity of that stand-alone title. Having discovered ghosts – having also discovered a fellow ghost-hunter in Nell West – he was keen, in his own understated way, to embark on more exploits. I was keen, as well, to explore the sometimes difficult, but gradually developing, relationship between the two characters.
So, from Property of a Lady came The Sin Eater, in which Michael and Nell uncovered the truth about a murderer who once prowled the fog-bound eeriness of Victorian London. After that was The Silence, inspired by childhood memories of a quiet house with apple-scented gardens, belonging to two spinster great-aunts who could spin enthralling stories out of their memories of Queen Victoria’s Diamond Jubilee and the Great War… And who played soft, magical music on the piano – music that might echo down the years to the present…
The Whispering followed, with the classic ghost-story setting of an old library in a remote house, and faded diaries and letters to hint at the secrets in its past. Then came Deadlight Hall, with its dark menacing echoes from the concentration camps of WWII. And most recently, The Bell Tower, the sixth in the series, set on the wild Dorset coast where uneasy memories of an ancient and sinister piece of music called Thaisa’s Song linger.
I’d like to think Michael and Nell’s relationship has developed throughout these books, and that they understand one another better than they did at the start. They’ve certainly had many a sunset-tinged romantic night, and around halfway through each book I wonder if I ought to write them into matrimony. 
But Michael’s place seems to be his book-lined study in Oriel College, with the tempestuous cat, Wilberforce, causing mayhem every other week. And Nell’s place is her shop in Quire Court, the cobbled square near to Turl Street, 
with the beautiful antiques that she loves buying and selling. So I don’t really think I can let the washing-up intrude on them quite yet.
http://www.amazon.co.uk/gp/product/B011M9L7D6/ref=series_rw_dp_sw