Season 4, Episode 1: Down by the River - Walt, Vic, and Ferg search for Branch, ultimately discovering Branch's body in a river, initially ruled a suicide. Walt's investigation reveals dirt in the shotgun shell, suggesting murder. The episode concludes with Branch's father, Barlow Connolly, confessing to killing Branch before dying in a "suicide by cop" attempt against Walt.

Season 4, Episode 2: War Eagle - Walt investigates Thorvin Hampton's death at a former Japanese internment camp, where he died of exposure. Hampton's father was a guard, and his half-niece, Shiori, confesses to locking him in, seeing it as retribution for her family's internment. Meanwhile, Walt continues to pursue evidence that Branch's death was murder, not suicide.

Season 4, Episode 3: High Noon - Jacob Nighthorse publicly accuses Walt of attempted murder. Cady's investigation reveals Barlow Connally's connection to Nighthorse, leading Walt to discover Barlow murdered Branch. Walt confronts Barlow, who confesses to killing Branch and Walt's wife, Martha. Barlow attempts to frame Walt, but Walt fatally shoots Barlow, bringing an end to the long-unsolved mysteries.

Season 4, Episode 4: Four Arrows - Walt returns, investigating a body found in a duffel bag after a casino bus crash, reluctantly seeking Nighthorse's cooperation. Henry, as Hector, helps a mother and son escape abuse. Walt dismisses Deputy O'Neill for a press leak. Walt solves the murder, and Henry secures the family's freedom.

Season 4, Episode 5: Help Wanted - Walt interviews deputy candidates while investigating robberies of stolen pharmaceuticals linked to a veterans' recovery group. He discovers desperate veterans are stealing antidepressants for their PTSD, leading to a tense standoff. Understanding their plight, Walt closes the case and hires Zachary Heflin as his new deputy.

Season 4, Episode 6: The Calling Back - Walt investigates the rape of Gabriella Langton by oil workers, facing significant jurisdictional hurdles. Cady seeks federal help, but scarce evidence and Gab's subsequent kidnapping complicate the case. Her mother accepts a deal, seemingly ending legal recourse. The episode concludes with a call for help from Hector.

Season 4, Episode 7: Highway Robbery - Walt investigates a deadly highway robbery where Peter Hoyt is killed and Jerry Napek is the sole survivor. Napek initially claims Hoyt was the victim of a casino-related loan shark. However, Walt's investigation reveals Jerry Napek murdered Peter Hoyt and staged the robbery. Walt ultimately arrests Napek after finding the hidden murder weapon and Hoyt's winnings. Meanwhile, Cady begins working on neglected legal cases on the reservation, and Henry prepares for his role as Hector.

Season 4, Episode 8: Hector Lives - Henry fully embraces his role as Hector, leading to the death of Will Balint, one of Gab's rapists. When the other rapist, Terry Malone, attacks another woman, Henry intervenes. Gab then shoots Malone to protect Henry. The episode concludes with Walt accidentally shooting Henry while pursuing a fleeing figure, leaving Henry's fate uncertain.

Season 4, Episode 9: Shotgun - Walt investigates the shooting of Tyler Malone and the arrest of oil rig worker Trot Simic. Meanwhile, an injured Henry goes on the run with Gab Langton, seeking a mysterious Crow Medicine Woman. Henry attempts to painfully remove a bullet from his own wound. The episode concludes with Henry collapsing after reaching the Medicine Woman's wheel, as shots ring out, leaving his immediate fate uncertain.

Season 4, Episode 10: What Happens on the Rez... - Walt faces pressure from Walker Browning, who seeks Gab and Henry. Henry, recovering from a gunshot wound, helps Gab escape with a false identity, while Mathias closes in. A confrontation with Browning leads to a shootout. The episode concludes with Henry being arrested by Mathias, who realizes he is Hector, and an unknown assailant kicking in Walt's door at his cabin.