The Enterprise approaches Neural, a planet in a far corner of the galaxy, home to two major settlements.  One tribe, nomadic, is called the Outer People; the other, the Central People, is agricultural.  As Kirk (the only one armed -- with a small phaser), Spock and Bones beam down, the Enterprise is called away to aid agents undercover on a planet engaged in civil war.  They materialize on the arid desert world and approach the village of the Central People.  As they near, they are alarmed to see warriors, dressed in the distinctive garb of the Outer People, guarding the village.  Even more alarmed when these guards open fire on them with rifles.

Kirk, Spock and Bones escape, though Kirk is slightly wounded.   As they run, Kirk's log narration fills in the back-story:  two years previously he visited Neural and left the two tribes co-existing in a shaky truce.  Ty-ree in command of the friendly Central People, and the war-like Apella in charge of the unfriendly Outer People.  Only these two leaders knew that Kirk was an "alien," only they know of the Federation.  Now someone has obviously interfered and raised these people above their bows and arrows and spears to the level of firearms.  Kirk determines to find his old friend Ty-ree and learn what has happened.

The three officers make their way toward what sensors indicate is the main grouping of the displaced Central People.  But the journey is hazardous -- searing heat and the "Neural Great Bear Creature," a predator rather like a cross between a grizzly and a hyena.  They hide in a crevice and escape the creature's attack.  Finally they reach Ty-ree's stronghold.  There we discover that the kind, gentle older man has taken a new young wife, Nona.  She eyes the strangers with distrust.

Ty-ree informs the landing party that a while back a "stranger" appeared and armed the Outer People with strange new weapons (rifles).  The stranger and Apella became fast friends and Ty-ree and his people were driven from their village.  They have taken refuge here in the mountains.  Ty-ree is relieved that his friend Kirk is here to set things right.

Kirk's slight wound has become infected -- he falls ill.  Ty-ree offers the services of his wife, who is adept at healing, using herbs and poultices.  She refuses to help at first but when Ty-ree reveals small details about Kirk after she cleverly pries and plies her feminine wiles, she agrees.  Nona cures Kirk and flirts with him in no uncertain terms.  Kirk, despite his knowing better, finds himself attracted to Ty-ree's woman.

The next day, Kirk is back on his feet, ready for action.   Kirk and Spock know very well it must be the Klingons arming Apella's people.  Such a lopsided escalation of power is an old trick of theirs.  They decide to scout and infiltrate Apella's village.  Nona, meanwhile, watches as her older, subdued, husband defers to the handsome young Kirk.  She scorns Ty-ree and shames him for his obsequious manner, and the old man reveals even more information about Kirk, though not meaning to.

At Apella's encampment, we learn that it is Kor who has been giving the rifles to Apella.  Apella wants even more, advanced rifles, but Kor is more interested in ideological conversions than mere casualty lists.

Kirk and the others sneak into camp -- Kirk sees Kor.  He realizes that he must do something to restore the balance of power.  Before they can sneak away,  Kor spots and recognizes Kirk.  Kirk and crew get away, and Kor realizes that he must attack the Central People quickly before Kirk can call in reinforcements.  Apella is angered when he realizes that Kor is acting solely for his own ideological purposes, not to help him defeat the Central People.

Safe in Ty-ree's tent, Kirk and Spock debate the merits of giving the Central People firearms.  The Enterprise has returned from its mission and Kirk orders the fashioning of rifles for Ty-ree's people.   The next day, Kirk, still tired and weak from his wound, sits on a lovely glen, relaxing.  Nona joins him, at first expressing only concern about his wound, but slowly inching closer until their lips are mere inches apart.

A SNARL -- another Neural Great Bear Creature attacks.  Nona is knocked down a hill, and the creature moves in for the kill.  Kirk pulls his phaser and kills the creature.  Nona looks at his weapon in wide-eyed amazement!  She leaps thousands of years of evolutionary development and realizes that with such a weapon SHE could rule all of Neural.  She promises Kirk that if he joins her they would both rule.  Kirk is not influenced.  Unseen by Kirk, Ty-ree approaches.  When Nona sees her husband, she grabs Kirk and kisses him passionately.  Shocked, Ty-ree turns and runs way.  Kirk pushes Nona away, but she smiles -- the damage has been done.

Ty-ree has disappeared.  Nobody knows where he went.  Kirk orders Spock to rendezvous with the Enterprise and deposit a cache of rifles in a hidden spot for use by Ty-ree and his people.  He then goes in search of Ty-ree, followed by Nona.

Meanwhile Apella leads the Outer People on a march to destroy the last of Ty-ree's people.  Kirk watches them march across the desert towards Ty-ree's encampment.

On a ridge above Kirk, Ty-ree fits an arrow to his bow, draws it back, aims dead-center on Kirk's back.  A moment, then he loosens the bow.  He cannot do it.

Enemy scouts close on Kirk and Nona.  Ty-ree aims and fires at them.  A pitched battle.  Kirk is stunned by a spear that grazes his head.  He drops, woozy, to his knees.  Nona grabs his phaser, dashes down the trail toward Apella's warriors.

Back at Ty-ree's encampment, the old chieftain laments that he does not deserve a beautiful young wife.  Kirk realizes his phaser is missing.  He must go after it.  He instructs Bones to lead the rest of the Central People to the point where the Enterprise and Spock will beam down the rifles.  Bones is to instruct the people on their use.

Kirk and Ty-ree rush down the trail in the direction Nona disappeared.  They find the discarded phaser and a bone-comb Nona wore in her hair.  It is obvious to both -- she has been killed by Apella's soldiers, and they, in their ignorance, have discarded the phaser.

Ty-ree is sure that his wife simply wanted a little more happiness, after all, she was always so very poor.  Surely, she was not evil, surely she did not want to join Apella.  Kirk tries to tell him that Nona was using him, using them all, but Ty-ree will not hear it.  Ty-ree again laments that he was not worthy of such a fine wife.  Kirk gives up trying to tell his old friend Nona's true motives.

They turn and walk away…

For years I had always assumed that Ingalls substituted his "Jud Crucis" pseudonym on this script for the softening of the Vietnam parallels.   While the aired episode's analogies are crystal clear, it seems that the major change was in Kirk's position.  The episode ends on an ambiguous note -- we will never know if Kirk actually ordered Scott to beam the flintlocks down or not.  We are left, perhaps, hoping that he has changed his mind.  Here it is stated in no uncertain terms.  Kirk aided in the escalation of war between these two tribes, who, left on their own, will most certainly annihilate each other.