The Bitterroots by C.J. Box

Cassie Dewell is making a good living as a private investigator in Montana after working for police departments in both North Dakota and her native Montana. When defense attorney Rachel Mitchell asks Cassie to investigate the case of Blake Kleinsasser, who's been accused of raping his teenage niece, Franny, Cassie is reluctant to get involved. Cassie feels Blake is probably guilty, but agrees to take the job because she feels that she is still in debt to Rachel after possibly being responsible for the decline in Rachel's father's health after they worked on a case together. The Kleinsassers are an extremely powerful family in Lochsa County, which also makes Cassie hesitant to participate. Soon, Cassie has more questions than answers as the people she talks to are secretive, evidence is missing, and she is threatened. The Bitterroots is a suspenseful ride as Cassie searches for the truth. A great read-alike for Michael Connelly.