Keyword Ray Weapons

Starship C57D travels to planet Altair 4 in search of the crew of spaceship "Bellerophon," a scientific expedition that has been missing for 20 years, only to find themselves unwelcome by the expedition's lone survivor and warned of destruction by an invisible force if they don't turn back immediately.

Test space rockets exploding at liftoff and increased reporting of UFO sightings culminate in a direct attempt by alien survivors of a dead, extra-galactic civilization to invade Earth from impervious flying saucers, using ray-weapons of mass destruction.