On planet Rexus, located on the far edge of the galaxy a distress call has been sent out. When an Allied Forces freighter arrives to investigate they find that everyone on the planet is dead or has left and the full content of the distress call is a warning to stay away from the planet. Unfortunately it's too late for the Allied Forces investigators, as a large force of alien creatures is spotted incoming on the radar. The only hope is to man the few remaining turret weapons left behind on the planet and destroy all waves of the attack.