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Captain Kirk must consider violating the Federation's prime directive -- non-interference in alien cultures -- in order to save a planet from destruction by civil war in this installment of the 1960s science fiction series. Visiting a familiar planet, the Enterprise discovers that the Klingons have instigated a violent conflict amongst the planet's two largest nations. By supplying arms to the stronger, more belligerent nation, the Klingons hope to unify and gain control of the whole planet. On the planet's surface, Kirk seeks out old friend Tyree, a member of the planet's more peaceful culture. Facing a complete rout, Tyree demands that the Federation even the battle by providing his culture with the arms to fight the superior Klingon weaponry. Kirk is torn between his belief in Federation non-interference policies and his loyalty to his friend and his peaceful civilization, and he must decide before the planet is devastated by total war.