Death Without Company
(book #2 of the Walt Longmire Mystery Series)
by Craig Johnson. This book brings the Basque community into the story when an old woman is found poisoned at the local home for assisted living. The investigation takes Walt and his team into issues of mineral rights, a 50 year old disappearance of an abusive husband, and an affair around the same time by the former sheriff, Lucian Connelly.
Lucian is one of my favorite charaacters. His character is played very well by Peter Weller (Admiral Marcus in Star Trek: Into Darkness.