Errand Of Mercy": This is the first time we meet the Klingons, the arch-enemies of the Federation. Kirk and Spock attempt to persuade the council of neutral Organia to join the Federation. While they negotiate, the nefarious Klingons invade and enslave the planet's sheep-like citizens. The Organians help Kirk and Spock disguise themselves as civilians, only to hand them over to the Klingons. The U.S.S. Enterprise and the Klingon ship poise to engage in an all-out battle. "The City On The Edge Of Forever": ...