Johnny Gibbs, Lucas McCain’s brother-in-law, visits the McCain ranch. Gibbs, a rodeo rider wanted by the law, begins stirring up trouble.
Mark comes down with typhoid after disobeying his father and drinking some polluted water. Lucas fears that his son may die, and a visitor in Mark’s dreams may be the only hope to save him.
From The Rifleman Episode Guide
Lucas McCain's late wife was Margaret McCain, and her brother Johnny was a rodeo rider wanted by the Law. After he settled his debt to society, Johnny may have started a family of his own, and his lineage may have led to Leroy Jethro Gibbs, a forensics investigator for the Navy (as seen in 'NCIS'.)
Most of Mark's memories of his mother Margaret may be based more on any pictures of her kept in the McCain home, but she seems to have a basic similarity in appearance to her brother. But when Mark had a fever dream in which his mother urged him back to the world of the living, she looked more like a "worldly" woman named Hazel who was part of a wagon train heading west.
"In case you haven't noticed,
Gibbs is a man of more questions than answers."
Dr. Donald "Ducky" Mallard