Captain Kirk leads a survey mission to a peaceful, primitive planet which he visited 13 years before as a lieutenant. He is dismayed to see a group of villagers armed with flintlock firearms, weapons they shouldn't have at their current stage of development. When the landing party beams down, Spock is seriously injured and is returned to the Enterprise for treatment as Kirk and McCoy try to make contact with the locals. They discover that the Klingons have armed villagers in hopes of eliminating the weaker hill people and allying the stronger warriors with the Klingons. To resolve the unfair advantage, Kirk supplies the hill people with flintlock rifles.

James Doohan (Lt. Cmdr. Montgomery Scott)
Nancy Kovack (Nona)
Michael Witney (Tyree)
Nichelle Nichols (Lt. Uhura)
Ned Romero (Krell)
Majel Barrett (Nurse Christine Chapel)
Walter Koenig (Ensign Pavel Chekov)
Booker Bradshaw (Dr. M'Benga)
Arthur Bernard (Apella)
Paul Baxley (Patrol Leader)
Gary Carpenter (Yutan)