A planet with no disease and no deaths appears to have kidnapped Kirk.
Kirk appears to be beamed down to Gideon, a planet that is free of disease and where the population is huge, but the Enterprise cannot find him. Kirk awakens in an empty replica of the ship, accompanied by a young woman named Odona. He learns that the Gideons are hiding a dark secret about their world.
The story is a mystery that unfolds slowly, with the Gideon government's plans only revealed at the end. It poses uncomfortable questions about overpopulation and the cost of a long life. Fans recall it for the stark twist about the consequences, and the puzzle of the empty Enterprise.