Story By: Nathan Butler and D. C. Fontana
Writer: D. C. Fontana
Director: Ralph Senensky

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

Leslie: Eddie Paskey
Leila Kalomi: Jill Ireland
Elias Sandoval: Frank Overton
Lt. Commander Kelowitz: Grant Woods

Stardate 3417.3

Omicron Ceti III is a planet exposed to Berthold rays which are deadly for humans when under long term impact. That is why the landing party expect all the colonists to be dead. To their astonishment they are not. In the opposite: They all are extremely healthy and, as Dr. McCoy finds out, their health is even better than it was before. The landing party are welcomed by Elias Sandoval and Leila Kalomi, a botanist, with whom Spock had worked together some years ago.

Leila had been very fond of Spock and is now glad to see him again. She now shows him a secluded section of the planet, where native plants are growing. As Spock get sprayed directly into his face with the plant's spores, Leila tells Spock that the plant induces feelings of harmony and peace and love. It also raises the desire to remain on Omicron Ceti III which then becomes like a paradise. The effect on Spock is the same - his defenses are lowered and he expresses his love for Leila and his desire to remain on the planet. 

Spock begins to enjoy the shapes of the clouds, the beauty of flowers and is not any more in the mood to answer his captain's orders via intercom. When Kirk finally founds his first officer, he almost can't believe his own eyes - Spock is dangling from a tree branch, enjoying himself like a kid. At the captain's anger Spock reacts with serene amusement. He tries to expose Kirk to spores, but they seem to have no effect on him. All crew members but Kirk experience the same emotional freedom on the planet and more and more beam down, since some of the spores have been brought on board. 

In the end Captain Kirk is the last who remains on the Enterprise. Sitting alone on the bridge spores of a plant which lies in front of him also explode directly into his face. He goes to pack some things and is about to leave for the planet. Leaving his ship ... the thought brings back all his senses. He becomes angry about everybody having left and experiences that anger destroys the effect of the spores. 

The lack of understanding by his best friend is the only flaw in Spock's new life. Telling Spock that he's coming down, too, but needs some help to bring things down which might be helpful for the people of the planet, Kirk talks him into coming on board. When Spock materializes, he faces his captain who's insulting him. First Spock stays calm and tries to convince him that he will calm down when he is on the planet. But when the captain's insults are aimed at his mother, he becomes angry and attacks Kirk. Kirk, who knows that the Vulcan strength cannot be met by human strength, has a hard time just to escape his First Officer's blows. Finally Spock realizes what he is doing - and the anger has destroyed the effect of the spores again. 

They clearly see that it is not possible to engage all people down there in a fight to eliminate the influence of the spores. When Spock wonders how to deal with the fact that two officers who have been engaged in a fight should be locked up, Kirk muses that if both were in jail, who would then make the staff return. Spock agrees. They then get the idea that certain sounds also create anger in people and flood the planet with sounds. Once the people are free from the spores influence, they decide to come back and life on board soon returns to normal. Leila is beamed up, too, and notices the change in Spock. She realizes sadly that he would not stay any more. Now the colonists see that the spores have prevented them from making any real progress. They plan to relocate where the plants do not grow. In the end, Kirk asks Spock about his experience and the Vulcan admits, "For the first time in my life, I was happy."