A visionary astronomer, Dr. Janos Rukh (Boris Karloff) has invented a telescope that can look far out into space â into the Andromeda Galaxy â and photograph rays of light that will show the Earth's past, something which he has theorized as possible for some years, to his discredit among his scientist-colleagues. Looking at the past on a planetarium-like dome in his lab, two of these ardently skeptical scientists, Drs. Benet (Bela Lugosi) and Stevens (Walter Kingsford), watch a large meteor hitting the earth, thousands of years ago at a spot in Africa. Amazed by the demonstration, the pair invite Rukh to go on an expedition to find the meteor.
While in Africa, Rukh finds the meteor but is exposed to its strong radiation, dubbed ("Radium X"), which causes him to glow in the dark, makes his mere touch cause instantaneous death, and will eventually destroy his mind, then his body. Dr. Benet develops a serum that holds this effect at bay, then takes a piece of the meteorite back to Europe, where he modifies its effects to help people, including curing the blind. Rukh returns to his jungle base and has Benet declare that he has heroically died in Africa, leaving his discovery to the world.
The situation has all along been complicated by the romantic relationship between his wife, Diana (Frances Drake), and Ronald Drake (Frank Lawton), the nephew of Lady Arabella Stevens (Beulah Bondi), Dr. Stevens' wife. As his mind deteriorates, Rukh become crazed with jealousy over Benet's success with his discovery, and returns to Europe and follows the others to Paris. Believing that he has died, Diana marries Ronald. Rukh begins to use the toxic radiation poisoning imparted to him by Radium X exposure to kill off the members of the expedition, and marks each death by disintegrating one statue outside a church across from his hideout by focussing his radiation through a raygun-like apparatus aimed out the window.
Rukh manages to kill each of the Stevenses before the police realize what is happening. They set a trap by convening a faux conference of scientists to discuss Radium X; but Rukh secretly gains access to the house and kills Benet also. He has saved Ronald and Diana for last, but finds himself unable to kill his wife, and this hesitation brings him to a confrontation with the one most-important woman in his life, his mother, who has all along foreseen her son's fatal flaws. She smashes the last of his antidote bottles as the radiation begins to consume him from within, and Rukh jumps from a window, being consumed by an explosive flame and vaporized by Radium X before reaching the ground.
Who is the visionary astronomer?
Dr. Janos Rukh