You are in command of Guardian, a powerful weapon which has been protecting Apollo, your home world, for generations. Your task is to defend against Dromeda, a starship of gigantic proportions, which has been attacking Apollo. Your home planet is protected by a force field which slowly deteriorates as it is hit by the enemy explosives. You must aim your lasers and destroy the explosives before they hit the force field. If your force field becomes weak enough, the first explosive that gets past it destroys your planet.