William Wellman Jr., son of the famous director, stars inProdigal Planet. Set in the future, the story concerns an ongoing battle against an all-powerful government organization called UNTIE. We first saw the good guys and bad guys inThief in the Night, then in two followup films. In this fourth entry in the saga, the forces of good do their utmost to bollix up UNTIEs complex communications systems. If this plot device smacks of a corny techno-nerd contrivance, please remember that virtually the same device was used in the megahitIndependence Day1996-and everybody swallowed it that time.