The unflappable Sheriff Walt Longmire and his deputies are trying to put the troubling events of the past behind them. The mysterious White Warrior who tormented Branch is dead. Walt's best friend Henry Standing Bear is a free man. Longmire's right-hand deputy Victoria "Vic" Moretti is newly divorced. And the mystery of Walt's wife's murder is seemingly resolved. But, the opening of the new casino on the Reservation brings dark new problems to Walt's...

The season premier picks up where the Season 4 finale ended. Walt is lying in his bedroom dazed from being shot by unknown assailants. After regaining consciousness in the hospital he sets out to find what happened to Dr. Donna Monahan, the psychiatrist that he started seeing in Season 4. Meanwhile Mathias blackmails Henry into continuing his charade as Hector - only aiding Mathias instead of innocent people.

A Wyoming sheriff struggles to cope with his wife's death as he attempts to move on with his life and career.