Rigelian Fever rages about the Enterprise; on a small planet named Holberg 917G, the crew has discovered a source of the only cure, ryetalin. Kirk, Spock and McCoy beam down, and discover the planet is the private property of Flint. At first uncooperative, Flint relents and permits the crew to gather the material. But events soon have them wondering about Flint's real goals, and his mysterious ward, the enchanting Rayna.