The Starion Cluster is under threat from the Pioneer Plague, which is spreading to every planet and destroying its lifeforms, having over-riden its original programming to merely transform uninhabitible planets into lush verdant lands for human colonization. The only solution is to fly to each of these planets and shoot out the pods from which the Plague hatches.
The gameplay essentially has 3 different sections. The main shooting action involves taking out as many of the pods as possible, while avoiding being shot by the Plague's self-generating protection robots. The more pods you destroy on each level, the easier the next levels will be.
Before each level you must fly to it through a mouse-controlled 3D section - completing the task quickly will again make your task easier. One unique feature is the ability to program the attack paths that your ship's two probes will follow when deployed - this is done by moving the joystick in the appropriate set of directions, producing five options which can be activated in-game.