Operation: Annihilate!

The Enterprise arrives at Deneva - the home of Captain Kirk's brother, Sam - and discovers that the entire planet has been infested with large, amoeba-like aliens that have attacked and killed much of the human population. One of these aliens attaches itself to Spock, who volunteers to become a subject in Dr. McCoy's medical tests. After McCoy accidentally blinds Spock during one of his test procedures, the doctor must quickly find a way to neutralize the dangerous creatures.[37]