Searching for the missing starship Defiant, the Enterprise eventually finds the lost ship enshrouded in a strange glow. A landing party beams aboard, finding that the entire crew of the Defiant went mad and murdered one another. While Kirk and the landing party inspect the Defiant, they notice the ship's solid surface are becoming ghost-like, while the crew of the Enterprise see the Defiant fading away. With the Enterprise's transporters confused by the fading, Kirk waits while the others beam back, but he cannot be retrieved as the Defiant disappears. Waiting for the next "interphase" during which the Defiant might return to the Enterprise's dimension, members of the crew begin to go insane, like the Defiant's crew. To make matters worse, a Tholian vessel arrives, and its commander refuses to believe that the Enterprise is assisting a damaged ship since the ship in question has disappeared. Tholians begin to weave a web of energy around the Enterprise, holding the ship in place as more of the crew lose their minds, and Spock and McCoy debate Spock's ability to command in Kirk's absence.
