Seemingly unfazed by the death of his parents, Don was an unwilling follower of the entity Gorgan. He, and the other children, were coerced by Gorgan to take the USS Enterprise to Marcos XII, to spread the evil entity's persuasion.
Shortly after the funeral conducted by Captain James T. Kirk, Don knocked over the United Federation of Planets flag planted by the burial site. He then apologized after Kirk cautioned him to be careful.
Later, while in the rec room, Don referred to Triacus as "that dirty old planet" after Kirk asked him whether he liked the Enterprise better, then replied to Tommy Starnes and Steve O'Connel's assertion that their parents did like the planet by noting that parents like stupid things. When the children started pretending to be bees, he asked Christine Chapel to guess what they were.