The Sad Man by P D Viner (sorry don't know how to do links but easy to find on Amazon)
This author has just published his first crime novel - The Last Winter of Danni Lancing - and The Sad Man is a free taster which links to the full-length book. Took about an hour to read and was really enjoyable - chilling and intriguing.
For those who like crime I recommend giving it a try