The spaceship AAB Gamma is dispatched from Japan to travel to Mars to investigate reports of UFOs in the area. When the Gamma nears the red planet, it comes across a mysterious alien vessel that sprays the ship with spores. Samples are taken back to earth where one of them begins to develop.
The cosmic spore grows into a giant, lizard-like creature dubbed “Guilala.” The monster begins a reign of destruction through Tokyo. It spits fireballs, feeds on nuclear fuel, turns into a flying, burning sphere and destroys any airplanes and tanks in its path. Guilala is finally defeated by jets laden with bombs, which coat it in a substance called “Guilalalium.” It causes Guilala to shrink down to its original spore form. The government promptly launches the spore back into space, where it will circle the sun in an endless orbit.