While visiting the newly discovered planet Phylos, Lt. Sulu picks up a walking plant, called a Retlaw, and is poisoned. The alien species that inhabit the planet, who are plantlike beings, approach and save Sulu's life. From them the crew discovers that most of the Phylosians were wiped out by a plague brought to the planet by Dr. Keniclius, a Terran scientist who survived Earth's Eugenics Wars . A giant clone of Keniclius, named Keniclius Five, kidnaps Mr. Spock in order to clone him and create an intergalactic peacemaker, at the expense of the original Spock's life. (Although Kirk never actually says "Beam me up, Scotty" in the series, in this episode he does say "Beam us up, Scotty.")