 The Enterprise is on a mission to a primitive, extremely warlike planet to negotiate a supply contract for a vital mineral. The party beaming down finds a Klingon has already gained the natives  trust; a crewman drawing his phaser is instantly killed. As the leader of their ten tribes hesitates which side to choose, there is a power-struggle and the Klingon s supporter takes over the throne, but respects Kirks military valor. Meanwile the Enterprise, incommunicado, learns an unarmed freighter is attacked by Klingons- Mr. Scott, in temporary command, leaves orbit to answer the distress call. McCoy touches a pregnant princess to diagnose her, and thus violates a taboo under pain of death- they manage to escape...