Episode 27. Errand of mercy (Stardate 3198.4): The Federation's archenemies, the Klingons, are introduced. While Kirk and Spock attempt to persude the council of neutral Organia to join the Federation, the Klingons invade and enslave the planet's sheep-like citizens. Episode 28. The city on the edge of forever (Stardate 3134.0): Accidentally overdosed on cordrazine, a delirious McCoy transports down to the planet below. Kirk and Spock follow and discover a "time portal" through which McCoy disappears. Entering the portal to search for McCoy, Kirk and Spock arrive in 1930 where Kirk falls in love only to learn the woman must die to return time to normal.