Too Close For Comfort - Adam Croft

What if the serial killer you were investigating was someone you knew?
DS Wendy Knight's first murder case was always going to test her limits, but even she couldn't anticipate that a sadistic serial killer might be someone she knew - very well.
As her investigation unfolds, so too does a sinister plot that will turn her world upside down and make it increasingly difficult to distinguish friend from foe in her tightknit world.
By the time Wendy realises she is the killer's final intended victim, she's left fighting against her personal instincts - and for her life.