Yellowstone's latest attack on the Dutton family ranch claimed the lives hundreds of livestock at the start of Episode 4, and the investigation as to who did it claimed its first human life by the end of the episode. "Only Devils Left" begun with the harrowing sequence of mysterious enemies dropping mysterious hay out of an airplane for the cattle at Dutton Ranch to eat. The next morning the workers awoke to hundreds of the ranch's livestock dead in the field.
John Dutton (Kevin Costner) immediately went into action, getting the wranglers to search the grounds as they got the sheriff's department on the case. However, given the family's history of causing trouble, it seemed as though the sheriff did not want to help them in their cause.
"So you think this was intentional?" John asks.
The sheriff, also listing the lack of tire tracks or other evidence pointing to a possible suspect. "You thinking that someone flew a plane over here to drop clover on your cattle in the middle of the night John? Think about that," the sheriff asks.
Jamie and John explain how someone could have been responsible for the crime.
When the sheriff says he doesn't have the jurisdiction, John encourages him to deputize his men so they can conduct the investigation themselves.
"You want to help? Give me deputies or deputize my men. Not in six weeks but right now. Right here in this field," John says, before suggesting Kayce (Luke Grimes) is the first one to be deputized.
After pushing the sheriff some times, John convinces him to give his men licenses to carry as livestock officers.
"If it comes out of your holster son, you better have an iron-clad reason," the sheriff warns, before John tells him he better send back up if his men need it during the investigation.
"We all know who did this, you find the evidence," John tells Jamie, then he tells Kayce. "When he does, drag him by the hair back to me."
The investigation doesn't take long to take a tragic turn, however, as Kayce and another livestock officer confront another rancher with a record and things quickly go awry.
After they discover that the man's report of slain cattle turned out to be a hoax, the officer tries to arrest the man, when his son comes out with a shotgun and threatens them. The officer freaked out in the standoff and shot the young man before Kayce could stop the situation.
Despite it being the officer's fault, John managed to spin the story in the news abut the sheriff's department not sending backup to prevent the tragedy. But the episode ended with the wranglers burning down the valley with the ranch's dead cattle, and the person responsible for the tragedy still at large.