As the Federation starship USS Enterprise circles the primitive planet Neural, which Captain Kirk has already visited, he and his First Officer Spock spot a group of locals readying an ambush. Shockingly, they have firearms, and their apparent target is a group of Hill People, with one individual, Tyree, being familiar to the Captain. Not being allowed to use phasers, Kirk tosses a rock at the villagers, which results in one of their guns being accidentally discharged. The pursuit that follows leads to Spock being shot.

As the USS Enterprise sailed around the ancient planet Neural, which Kirk had already visited, he and Spock noticed a bunch of natives preparing an ambush. Surprisingly, they were armed with guns and seemed to be targeting a group of Hill People, one of whom the Captain recognized, Tyree. Despite not being allowed to use phasers, Kirk threw a rock at the villagers, which unintentionally made one of the guns fire. Unfortunately, this led to Spock getting shot.

Afterward, a friendly group of Hill People accompanied Kirk and McCoy to their camp, where Kirk learned that Tyree had become their leader. Tyree married Nona, a Kahn-ut-tu woman who could heal the Mugato bite. Nona had been encouraging Tyree to acquire firearms for their tribe.

When Nona heard Kirk's arrival, she snuck into the cave and noticed McCoy utilizing his phaser to warm some stones. She was awestruck and questioned Tyree about the peculiar visitors. Then, she tended to Kirk's wound by pressing a Mahko root with her cut hand before the ritual started. After the ceremony, she declared that Kirk was now hers, and Tyree told her that, as per the legend, Kirk would not be able to reject her after the treatment. Miraculously, both Kirk and her hand were fully healed.

When Kirk regained his strength, he inquired Tyree about the villagers' arms. Tyree revealed he had encountered them for the first time a year ago and assumed the villagers had crafted them. Consequently, Kirk and McCoy planned to scout the village that evening. After arriving, they identified a forge with a chrome steel drill and almost pure iron, hinting at the participation of outsiders. Soon enough, a Klingon showed up with the village's leader in tow, and they began talking about the production of upgraded weapons. Again, Kirk and McCoy took them by surprise and overpowered them, seizing a flintlock weapon before fleeing with Tyree's assistance.

The following day, Kirk demonstrated how to use the weapon to the Hill People, but Tyree staunchly refused to get involved. McCoy expressed his uneasiness, but Kirk stated that both rivaling sides must be on the same level to make it through. Nona attempted to lure Kirk with the help of local herbs. Nevertheless, a Mugato attacked Nona and Kirk eliminated it with his phaser. Nona then knocked Kirk out, escaped with the phaser, and attempted to give them the weapon upon encountering a group of villagers. Not believing her story, they attacked her. When Kirk, McCoy, and Tyree arrived, the villagers thought she had led them into a trap and killed her. The two groups engaged in a fight, and the villagers ran away.

Tyree insists on being equipped with additional "fire stick" firearms to avenge his wife's passing. Kirk hesitantly orders Scott to construct and transport a hundred flintlocks to the indigenous people. Scott queries the unique mandate, to which Kirk responds, "Weapons for the Garden of Eden."