The last of its kind is destroyed, leaving the Enterprise to sail into the stars with a heavy heart, mourning not just their lost crewmen, but the extinct race they were forced to end.
As Kirk investigates, the "Nancy" aboard the ship begins a lethal game of hide-and-seek. She is actually the last of a shapeshifting species—a "Salt Vampire"—that survives by consuming sodium chloride from living beings. It maintains its disguise by telepathically projecting an image from the observer's own memory or desires. The Man TrapStar Trek : Season 1 Episode 1
The USS Enterprise arrives at planet M-113 for a routine medical delivery to Dr. Robert Crater and his wife, Nancy—an old flame of Dr. McCoy. While Kirk and Spock see an aging woman, McCoy sees the vibrant beauty he remembers from ten years ago. The last of its kind is destroyed, leaving