Martians are attacking the Earth and planning to destroy all life in it. A Martian space ship is orbiting the earth and a big laser cannon is being built on Earth and it is the player's mission to hold the Martian threat until the laser cannon is complete. To do so, the SIDO (Space Intruder Defense Organisation) infiltrated a fighting probe inside the Martian spaceship.
In Martian Threat, the player controls a fighting probe with the joystick. The lack of gravity will make the probe keep moving until reverse thrust is given. The player has to shoot Martians and their energy bombs, which will appear in four different spots.