The Enterprise ferries a spoiled but dangerous princess to a political marriage as Klingon ships close in.
The Enterprise carries Elaan, a headstrong princess of Elas, to her wedding with the leader of the Troyians in order to end a long war. Elaan's tears carry a chemical that makes any man fall in love with her, and Kirk is affected as the Klingons close in on the ship.
The episode is a story of diplomacy and temptation. It reveals Kirk's will in resisting, and also shows the damage done to the ship. It is a rare Trek story that involves royalty, and fans remember the combination of romance and space battle, as well as the effect on the captain.