Relentless Pursuit is the third and final book in the Secrets of Roux River Bayou trilogy, following False Pretences and Dangerous Mercy, and begins two years after the events in Dangerous Mercy. While the main mystery plot is a stand-alone story, the subplot is related to the characters from the previous books, so it would help to read them in order. I read Dangerous Mercy and Relentless Pursuit books back-to-back, which made it easier to keep track of the multitude of characters.More murders are occurring in Belle Fourche, this time as a result of poison injected into locally-bottled water. This gives the police two problems: catching the culprit based only on a grainy security camera photo, and ensuring that all the bottles of water sold are located before anyone else dies.While the murder hunt is going on, there is a visitor in town - Zoe’s brother, who has returned to find the sister he abandoned many years ago. They had an abusive father, and Zoe has to work on forgiving her brother for not taking her when he left. Even though she has been a Christian for many years, she still find this difficult.Overall, I enjoyed this series, even though the concept of a murder mystery where the police force where not the main character was a novel concept (if you will excuse the pun). The books are well-written, the characters are strong and likeable, but not perfect, and the setting is well done. These are solid mysteries with underlying themes of faith and forgiveness. Kathy Herman is now working on another trilogy, Tales of Foggy Ridge, which will be set in the Ozark Mountains of Arkansas, and will contain some characters from this series. Thanks to David C Cook and NetGalley for providing a free ebook for review.