A pair of astronauts encounter an alien civilization while exploring the unknown Planet X. The Xians request their aid in fending off Monster Zero, known on Earth as King Ghidorah, and ask to borrow Earth's mightiest monsters in order to defeat him. After constructing a plan, Godzilla and Rodan are shipped off to Planet X, but something nefarious is at foot... In truth, the Xians plan to control the monsters using magnetic waves in an effort to conquer the planet, and it will take all of Earth's forces to stop them! This sixth film in the Godzilla series introduces more science fiction elements than ever before in a space-opera of epic proportions. American actor Nick Adams would co-star as Astronaut Glenn Amer in Toho's continuing effort to reach a widening audience over seas. Adams is joined by Akira Takarada, and together they make an enjoyable team on screen. Once the monsters return to Earth under the control of the Xians, the destruction and carnage is unmatched as they obliterate more of Eiji Tsuburaya's finely-made models. In a moment that fans are unlikely to forget (or forgive), Godzilla performs a child-like victory dance after he and Rodan first defeat Ghidorah while on the surface of Planet X. INVASION OF THE ASTRO-MONSTER is another excellent sequel and an important stepping stone in the evolution of the Godzilla series.