A group of energy beings attempts to take over Lt. Mira Romaine, a memory-alpha specialist.
The Enterprise delivers equipment to the Memory Alpha library planet and encounters a strange storm of lights. Lieutenant Mira Romaine, who is on board as a technician, is taken over by the beings, and Scotty, who has fallen in love with her, tries to save her while the others attempt to understand what the visitors want.
The story gave Scotty a rare romantic subplot and introduced the Memory Alpha library, which later appeared in other stories. Fans remember it for Mira's dramatic scenes and for its use of a pressure chamber, which shows the courage and the heartbreak of the chief engineer.