Executive producer: Gene Roddenberry
Associate producers: Edward K. Milkis and Gregg Peters
Producer Fred Freiberger
Co-producer: Robert H. Justman
Story consultant: Arthur H. Singer

Story by: Gene Roddenberry
Writers: Gene Roddenberry and Arthur Heinemann
Dir.: Herschel Daugherty

Captain Kirk: William Shatner
Science Officer, First Officer, Cmdr. Spock: Leonard Nimoy
Dr. Leonard "Bones" Mc Coy: DeForest Kelly
Lt. Sulu: George Takei
Lieutenant Commander Montgomery Scott: James Doohan
Lieutenant Uhura: Nichelle Nichols
Abraham Lincoln: Lee Berger
Barry Atwater: Surak
Yarnek: Janos Prohaska
Genghis Khan: Nathan Jung
Kahless: Robert Herron
Voice of Yarnek: Bart LaRue

Stardate 5906.4

Excalbia, a planet with a hot surface of melted, hot lava is surveyed by the Enterprise as they suddenly detect an energy field coming from the planet. In front of the ship appears a very friendly Abraham Lincoln sitting in his armchair and inviting himself to come on board. Finding this quite impossible to be true all are puzzled, but Kirk decides that Lincoln will be welcomed and orders the officers to put on official gear to treat him as a guest of honor. A real gentleman, Abraham Lincoln is absolutely polite and caring and invites them down to the planet. Indeed, Spock detects a place where normal living conditions are found in spite of the hostile rest of the planet. 

After a discussion with doctor McCoy, Kirk states that their prime duty is to research new phenomena and this is exactly what he decides to do in spite of the odds. Lincoln cannot precisely say what will be ahead of them, but he is convincingly caring and interested in having them as guests. On the planet Kirk, Spock and Lincoln meet Surak.. Surak was the founder of Vulcan philosophy, the IDIC and of the peaceful development of the planet. Surak greets Spock and shares his wish that the greeting should be returned. Spock greets "the image of Surak". Surak finds Spock having an emotional moment (which could not be detected by any untrained or non–Vulcan eye). Spock agrees and apologizes. But Surak says that he understands this under the given circumstances. 

All wonder what made them come here as suddenly Yarnek, a rock–being, greets them. He/she introduces himself/herself and explains the purpose of the gathering: Her/his race needs to find out which of the human ways, good or bad, is better to live by. The being introduces to them four other guests (Zora, a criminal scientist; Genghis Khan, a tyrant of ancient Earth; Colonel Green, a serial killer, and Kahless, the founder of the Klingon aggressive way of reaching purposes by war or fighting), whom they are going to fight. Since they cannot be beamed up by the Enterprise, they are left on their own even without the phasers. 

Totally convinced that only talks and peace are acceptable ways of solving problems, Surak informs his three partners that he will go and talk peace. Kirk cannot prevent him to go and again Surak states that he will never fight. While they prepare spears by using branches and stones, they hear Surak cry out loud for help. Kirk wants to go to help him, but Spock keeps him back: Surak knew the risk and he assures the captain that a Vulcan would never scream. Now Lincoln also cannot stand the cries for help and suggests a plan. 

Because this is obviously a trap, he suggests that Spock and Kirk attack from one side while he tries to free Surak coming from behind. Both attack. The moment Lincoln reaches Surak who's sitting on the ground bound to a bush, he hears Surak's voice behind him: Kahless has imitated Surak's voice all the time Surak was already dead. The four have now got him, too. In the final close fight Kirk and Spock overcome their counterparts and Yarnek removes the others from the scene they had built for them. Yarnek says that they still have to decide which side to turn to, because both sides have used nearly the same plots and weapons. Kirk and Spock are returned to the Enterprise, where they contemplate the situation. They had seen Lincoln and Surak exactly the way they had imagined them to be.