Planet X is a synthetic industrial planetoid whose most notable feature is the research laboratory of the buxom and brainy Dr. Sarah Bellum. Evil aliens called Reptilons invade the planet, capture the good doctor, and force the rest of the humans to manufacture a robot army to take over the Earth.

The player must shoot their way through a series of maze-like levels, releasing the human hostages along the way. Levers must be found and thrown to activate the escalators which allow access to new areas. Gems can be collected to increase the power of the player's ray gun, and food lockers may be broken into for a health boost.