Gary Mitchell is dead, killed by his best friend for the sake of his ship. As Captain Kirk returns home in sadness, he recalls the first time he held Gary's life in his hands. The time is seven years earlier, and the two men have been assigned to the USS Constitution, Gary as chief navigator and Kirk as second officer, when the starship comes to the defence of an alien world menaced by ruthless invaders. An early attack leaves both the captain and the first officer in comas, and Jim Kirk must take command for the first time. He finds himself with only one chance to defeat the heavily armed enemy - but the cost may be Gary Mitchell's life!