Jantor is the name of the harsh and desolate planet that lies half in this dimension, and half in another. The strangeness of this shadow world is a result of the presence of large quantities of tricasmium; a rare ore with subtle and unusual properties. A Rigillian fleet has been sent to conquer Jantor, and only your Space Hornet interceptor can stop it.
Shadow World is a mostly side-scrolling shooter, ala Defender. Rigillian crystal ships slowly descend from the sky, and can only be defeated by having their central core destroyed using your interceptor's plasmatronic cannons. These crystal ships deploy a skimmer, which retrieves tricasmium from the surface, allowing the ships to descend safely. They also deploy guardian drones which act as escorts. Once a crystal ship reaches the surface of the planet, it becomes a colonizer and impervious to weapon fire. The colonizers can only be inactivated by picking up a tricasmium nugget and then flying over the entrance of the colonizer.
Your interceptor is armed with a small number of smart bombs, which obliterates enemies on the screen and returns you to your base. Successful destruction of each waves of ships rewards you with another smart bomb. Armed with cannons and these bombs, you must prevent five active crystal ships from landing, or the entire planet will be sucked into a temporal vortex.