A mysterious, planet-sized energy cloud is heading for Earth, destroying everything in its path. Admiral James T Kirk returns to the bridge of the Enterprise to stop the invader, but he has to contend with a bitter rival and the possession of one of his crew by the alien force. Sci-fi adventure, the first movie based on the TV series, starring William Shatner, Leonard Nimoy, DeForest Kelley and Persis Khambatta