A man must save his brother from the bloodthirsty mob that wants him to hang for a crime he didn't commit.
Both Sprague and Jett and their crews are hunting buffalo. Doan is with Sprague and is looking for the Jett outfit where his girlfriend Milly is being held against her will.
The "trailer" is a dog named Caesar and the killer is a mountain lion, aka as a cougar or puma the narrator was quick to point out.