In the 24th century, Earth is pounded by solar explosions and abandoned by humans, and the planet is recolonized by a dangerous race known as Kat Men. When the solar explosions died, the humans decide to return to Earth. When the Kat Men refuse to leave, a war droid known as MT-ED, or Multi Terrain Exploration Droid, is sent down to deal with the Kat Men. Accompanying him is Hercules 1, a maintenance and combat droid. When the two droids are beamed down, things take a turn for the worse. Hercules is kidnapped and taken far away to the Kat Men's Nerve Center. It is MT-ED's task to get rid of the Kat Men and rescue Hercules.
To do this, MT-ED has to explore fourteen environments and deal with deadly creatures that are within each environment, with each type of creature requiring a certain type of weapon to be defeated. These weapons - including lasers, water bombs, grenades, and rockets - can be picked up along the way, and MT-ED can switch between them with ease. If MT-ED comes into contact with any of the creatures, he is kicked into the air and gets stunned for a few seconds. If this happens, he loses one of his lives. Not all creatures are deadly; some of them will steal whatever weapons MT-ED is carrying at the time.
Besides using weapons to kill, MT-ED also has the ability to jump over creatures that may be too slow for him to shoot. When MT-ED finally rescues Hercules, a sub-game needs to be completed. When MT-ED completed this sub-game, the Kat Men's Central Computer is disabled and the Kat Men go back where they came from.