The player is a spaceman with a jet-pack, flying across a barren landscape whose skies are inhabited by a number of different aliens; from the simple Planter to the slowly advancing Blunder Storm or the quick, aggressive Nemesite.

The action takes place on the moons of Jupiter, as well as on Jupiter itself. At the last level on each moon the player has to defeat a planet guardian. To do this the player has to hit them in their glowing green nerve centre that is exposed at times as they move around. Each wave starts with all remaining humans being beamed up by a leader enemy and to release the men it has to be defeated.