Leila Kalomi, an old friend who had been (and still is) in love with Mr Spock. She leads Spock into being affected by the spores, and he is thereafter, for the first time, able to express love for her in return.
Spock and Leila, also a scientist, first met on Earth six years before TOS, where she fell madly in love with the unreachable Vulcan. But as with Christine, the feelings were one-way. But in This Side of Paradise they encounter one another again on Omicron Ceti III.
Leila is determined to have him stay, and this time, she has help. The planet's native spores free their hosts of inhibitions and provide a sense of peace and belonging, which Spock finds agreeable. Once affected Spock declares " I love you!" but then revises this: "I can love you!" They kiss, frolic in the woods, and contemplate clouds.
As the couple prepares for their new lives, Kirk is determined to win back his mutinous crew, starting with his first officer. He beams the unsuspecting Vulcan aboard the ship, hurls insults, and starts a brawl, negative emotions being the "cure" to the spores. Spock realizes his true place will always be on the Enterprise bridge and parts ways with the teary-eyed but sympathetic Leila. Spock says of the planet only that "for once in my life, I was happy."
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