The Enterprise traces a virus-like outbreak that seems to be traveling in a direct line across a planetary system. The next planet is home to Kirk's brother Sam, his sister-in-law and their young son. The Enterprise arrives too late however for Sam. They find flying jellyfish-like creatures that attach themselves to humans. They take over the victims nervous system forcing them to bend to their will. Spock finds a weapon to use against the creatures but it leaves him hopelessly blind. Written by
Did You Know?
Some non canonical Star Trek novels have given the explanation that Sam Kirk's two other sons (spoken of in What Are Little Girls Made Of) were away from Deneva during the events of the episode. It has also been suggested that Sam Kirk having three sons was part of the misinformation Kirk planted in his robot double in What Are Little Girls Made Of. See more
When Spock stuns the creature to take as a specimen, it lands face down, but close-ups show it face up. See more
[Spock, infected, beams down to the planet to collect a specimen
Jim, that man is sick - and don't give me any damnable logic about him being the only man for the job.
I don't have to, Bones. We both know he is.