A lieutenant in the Enterprise-D's engineering department who is killed when a distortion in a dark matter nebula briefly makes the deck beneath her insubstantial.
Lieutenant Van Mayter is an engineer aboard the USS Enterprise-D who appears in the fourth-season episode In Theory, set in 2367.
While the ship surveys a dark matter nebula, odd things begin to happen: objects are found moved or fallen, and sections of the ship lose atmosphere for no clear reason. Van Mayter is helping to track down the faults when she is found dead in a corridor, her body sunk halfway into the deck plating as though the floor had closed around her.
Her death shows the crew what they are dealing with. Pockets of deformed space in the nebula cause solid matter to phase out for an instant wherever they touch the ship. The discovery prompts Picard to take a shuttlecraft ahead and lead the Enterprise out by hand.