When Lt. Austin receives a strange fax of the itinerary for someone called "Sheppard", she and Commander Rabb don't realize the seriousness of this fax. Later, Austin is shot and critically injured while at JAG headquarters by the person who accidentally sent the important fax to the wrong number. Rabb learns the shooter must be the infamous assassin known as "Hemlock;" a person that no one has seen long enough to give a description. Now, Rabb must find out Sheppard's true identity in order to find the assassin before he strikes again.
After being diagnosed with night blindness, Lt. Cmdr. Harmon Rabb, an F-14 Tomcat fighter pilot, is forced to change careers. Cmdr. Rabb chooses to join the Navy's Judge Advocate General (JAG) Corps. There he both defends and sometimes prosecutes Navy and Marine Corps defendants. He is sometimes assisted by fellow lawyer, Lt. Sarah "Mac" MacKenzie, and his other fellow JAG staff.
Many of Rabb's cases require him to both keep up his F-14 qualifications and travel the world, in order to bring justice to the cases he is trying.
Rabb must also deal with the fact that his father, also a former Navy pilot, never returned home after being held prisoner after he was shot down in North Vietnam. Rabb believing his father is still alive continues the search he has pursued to find his father, since his teens.