Executive Producer: Gene Roddenberry
Producers: Gene L. Coon + John Meredyth Lucas
Associate Producer: Robert H. Justman
Script Consultant: D. C. Fontana

Writer: Theodore Sturgeon
Dir.: Joseph Pevney

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
Nurse Christine Chapel: Majel Barrett

T'Pau: Celia Lovsky
T'Pring: Arlene Martel
Stonn: Lawrence Montaigne
Admiral Komack: Byron Morrow

Stardate: 3372.7

Spock experiences a difficult time. With all his strength he tries to control himself and hold back illogical actions, but the changes inside him are so strong he cannot suppress them efficiently. Dr. McCoy examines him and finds him undergoing extreme internal changes which might kill him eventually.  For Spock it is difficult to talk about the situation. It is too private and especially for a Vulcan nearly impossible to discuss pon farr with a non Vulcan. Pon farr, the mating cycle, goes along with plak tow, blood fever, and occurs every seven years in a Vulcan to force him to choose a mate -or die. It takes Spock a lot to share with his friend the implications of the cycle Vulcans hardly ever talk about. Spock had hoped his Human half might prevent pon farr in him, but it proved to be different: He is bound to get to Vulcan and marry T'Pring, his wife with whom he was engaged since they were 7 years old. 

The choices to overcome the crisis are to marry or to die. Spock suffers from knowing that the crises he is in cannot be handled by logic. Spock had not eaten since days. Nurse Chapel, who has cooked a ploomik soup for him (apparently it takes days to prepare this meal as the doctor notices) tries to make Spock eat the nutritious Vulcan food.  She escapes out of his room, crying, the bowl of soup flying after her. Now Kirk is sure: His friend is under tremendous stress. Kirk is now under pressure, too. His orders are to continue the Enterprise's journey without delay. The Enterprise is expected on Altair VI to attend inauguration ceremonies. Trying to convince the representatives of the Federation, he gets the strict order to maintain course. But he has not forgotten what Spock had done for him and for the Enterprise and decides to go against orders. 

On Vulcan they are greeted by T'Pau. She is the only person ever having declined a high position in the Council of the United Federation of Planets. Her presence indicates the high importance of Spock's family Spock never talked about. They are welcomed by T'Pau who uses the Vulcan greeting and Spock asks permission for his friends, Kirk and McCoy, to stay at the koon-ut-kal-if-fee (the place of marriage or challange). T'Pau allows and submits them to obey Vulcan rules and laws. To initiate the marriage procedures Spock begins with the rites .... and is interrupted by T'Pring. She makes use of the ancient laws which give the women the right to choose. An exception which is hardly used because the choices are logical and the partners usually are in mental contact with each other over the years. 

The only alternative to the planned marriage is a combat between the groom and the person the woman chooses. T'Pring passes Stonn, who's obviously waiting for being nominated her choice. McCoy talks to Jim and tells him Spock has no chance in his present condition against another Vulcan who's not in pon farr. But T'Pring passes him and stops before Kirk. Captain Kirk is her choice. Kirk agrees intending to give Spock an easy win. Only after having agreed Kirk learns this fight is to the death. Spock is deep into plak tow, his blood burning and his mind concentrated on fighting the rival man. Nevertheless he manages to speak and tries to convince that T'Pau he does not want to fight his friend. But the rules are clear and they have submitted to the laws. 

Quickly Kirk discovers he's encountering an opponent in trance. Spock sees the rival in him and the blood fever prevents him from seeing the friend. Kirk survives the first round, where a sharp weapon is used, by luck and finds Spock's Vulcan strength as overwhelming as ever. And he sees Spock's blind determination to win. McCoy intervenes. Asking T'Pau to allow him to inject Kirk a substance to adjust his body to the Vulcan condition of the planet’s atmosphere and injecting Kirk McCoy contributes to the end of the fight: The next part of the fight involves a sling, a deadly weapon when used by an experienced fighter. Kirk finally dies when Spock strangles him. 

All tensions are over and the pressure inside Spock is gone after the fight. T'Pring is now Spock's wife. He sets her free because she made him fight but asks her to explain her action. She points out that Spock has become a legend and she does not want to be married to a legend. She wants Stonn and she would have him anyway either Spock set her free or he would be gone. In case Kirk had won, he had not wanted her and she could have Stonn, he would be gone, too. Spock calls this logical and does not show any feelings when he tells her that sometimes the things we wish for might not be as desirable any more when we have them. This wisdom from earth may not sound logically but it is often true, Spock says. T'Pau wishes him "Live long and prosper" and Spock answers that none can be achieved any more since he has killed his captain and his friend. 

Back on the Enterprise Spock informs McCoy he steps down from his duties since he has killed his captain. McCoy's answer is a smile. He sees Kirk coming from behind Spock's back and asking Spock.: "You have killed me?" Spock swings around, grabs Jim at his shoulders and is overjoyed – a logical reaction of relief after what he is gone through. McCoy explains he's given Kirk a knockout drug and not a tri-ox compound as stated. Both muse about Spock's reaction hiding their understanding. Star Fleet Command approved of the Enterprise's diversion of the flight route after T'Pau has requested the Federation to divert the course of the Enterprise via Vulcan.