You start the game with three Marauders. When your third Marauder is killed, the game is over.
You've landed on an alien planet and penetrated the enemy base defended by armed attack robots. Your mission is to find your way to the heart of the base and to destroy the power center of the enemy's weapon system. Robots pursue you through halls and corridors, from room to room, as their sensors detect your presence. They fire at you from all corners. It's a race against time to find the power center as you shoot back, defending yourself against the onslaught.
There are four difficulty levels which determine the speed at which the robots shoot and maneuver. Each leveel starts with four robots per room. When you destroy the power center the first time, you play at the same level but with five robots per room. When you destroy the power center a second time, you play with six robots per room. The next time, you advance to the next difficulty level with four robots per room. Then five robots, then six. This provides 12 combinations of difficulty based on the robot speed and numbers.