The Enterprise shuttlecraft, carrying Kirk, Spock, Dr. McCoy and critically ill Federation Ambassador Nancy Hedford, encounters a mysterious energy cloud which pulls them down to planet Gamma Canaris N. There they meet a castaway, a young man who purports to be Zefram Cochrane, inventor of the Warp Drive over 100 years ago. In history he had lived to be 80 years of age before disappearing somewhere in space. Apparently the same energy cloud which brought the shuttlecraft to the planet also found and rejuvenated Cochrane, making him effectively immortal. Unless Kirk can get themselves released soon, the ambassador, without vital medical treatment, will die.