The nostalgia is quickly cut short when a crewman is found dead, his body drained of all salt.
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 climax shifts back to the ship, where the creature corners McCoy in the guise of Nancy, pleading for his protection. Even as Spock is attacked and Kirk shouts for him to fire, McCoy hesitates, unable to shoot the face of the woman he once loved. It is only when the creature reveals its true, horrific form and begins to drain Kirk that McCoy finally pulls the trigger. The nostalgia is quickly cut short when a
The creature stalks the corridors of the Enterprise, claiming more victims by assuming the forms of various crew members. Back on the surface, Spock and Kirk discover the real Nancy Crater has been dead for years; the Professor has been "feeding" the creature salt to keep it calm, treating it like a pet out of loneliness and grief. It maintains its disguise by telepathically projecting an