I nominate Thin Blood
by Vicki Tyley. I've heard many strong compliments about this author and I'm reading this book this month anyway.
Craig Edmonds, a successful stockbroker, reports the disappearance of his wife, Kirsty. What starts as a typical missing person's case soon evolves into a full-blown homicide investigation when forensics uncover blood traces and dark-blonde hairs in the boot of the missing woman's car. Added to this, is Craig's adulterous affair with the victim's younger sister, Narelle Croswell, compounded further by a recently acquired $1,000,000 insurance policy on his wife's life. He is charged with murder but, with no body and only circumstantial evidence, he walks free when two trials resulting in hung juries fail to convict him.
Ten years later, Jacinta Deller, a newspaper journalist is retrenched. Working on a freelance story about missing persons, she comes across the all but forgotten Edmonds case. When she discovers her boyfriend, Brett Rhodes, works with Narelle Croswell, who is not only the victim's sister but is now married to the prime suspect, her sister's husband, she thinks she has found the perfect angle for her article. Instead, her life is turned upside down, as befriending the woman, she becomes embroiled in a warped game of delusion and murder.
Currently $3.99 at Amazon.