I'd like to add to George-841's review. This is indeed an episode with wasted potential.
One of the problems with pre-cable networks is that action/adventure programs tended to have violent resolutions. The villains are usually beaten to a pulp or killed. Though there are many good things to say about "The Rifleman", the series too-often falls back on the easy way out, with bloody endings. (As McCain can fire his rifle quite rapidly, more than the usual quota of bad'uns are disposed of.) Given that "The Rifleman" sometimes had unexpected or surprising endings, I was hoping this one would, too. It didn't.
Chaqua has kidnapped Mark to replace his own son, who died not long before. The audience knows Mark isn't going to be eliminated in the first season, so the given ending is an foregone conclusion.
A much-better ending would have had McCain and Chaqua confronting each other over the campfire, with McCain convincing Chaqua that a 10-year-old boy isn't likely to adapt well to Apache life, and that Chaqua should not be causing two people grief just to ease his own. After extreme internal conflict, Chaqua reluctantly agrees and returns Mark.
This could have been further developed, by having Chaqua "adopt" Mark as a surrogate son, with Mark occasionally visiting him (in future episodes) to learn things his father couldn't teach, and get a broader view of the world.