The plot involves a sinister Captain who brings prosperity to his people by doing something really evil -- and I won't tell you what it is for fear of giving away the plot.
The budget for special effects and sets for this series must have been about fifty pounds per episode (makes the original Star Trek series look slick in comparison) but for a true Dr. Who fan, the cheesiness of the sets only adds to the charm. This video has a classic laughably funny scene, with a ride in an "air car" that is obviously a cheaply constructed prop tilted to one side, with a blue back drop, and a fan blowing on the characters to imitate flight. But there are also some very witty lines, beautifully delivered by Tom Baker and others in the cast.
If you collect Dr. Who videos, this one is a "must have."