The sixth installment in the Star Trek original series, The Abode of Life.

The citizens of the planet Mercan cannot conceive of worlds beyond their own. Their sun is prone to deadly radioactive flare-ups, and the Mercans have organized their life around the need to survive The Ordeal. All that might change, though, when a badly-damaged EnterpriseTM arrives near Mercan, desperately in need of repairs. It's not an easy task, though, begging help from people who can hardly believe in your existence, and Kirk finds himself torn between the safety and survival of his crew and the Prime Directive, which dictates that he must leave the Mercans to live their lives in peace, and, therefore, in ignorance.