As the last human left on the fortress planet of Roolfhtenin it is your mission to delay the evil forces of Crabok for as long as possible. You have three laser bases at your disposal with which to shoot the hoards, but the longer you survive the faster the aliens will attack with waves of dive-bombing ships. They have unlimited forces; all you can do is buy time.
Once the game has loaded, press 3 to start playing. The instructions for moving the laser base will appear on screen.