Dr Janos Rukh (Boris Karloff) is a reclusive scientist working in his Carpathian Mountains home on a project that he believes will be of great benefit to mankind. Tonight - a dark and stormy night - he has invited a group of people he hopes will have great interest in his theories and has asked his wife Diana (Frances Drake) to keep a lookout for the headlamps of their vehicle. She stands at the window, deeply concerned, talking with her blind mother-in-law about Rukh's mental health. Then, the lights appear and Diana rushes down the corridors to the laboratory and observatory where her husband, who was much admired by her late father, conducts his work. He will have surprising things to show his visitors, but what can be a boon to humanity can also be a curse...
By the mid-nineteen-thirties, Boris Karloff (billed here as just his surname, such was his fame) and Bela Lugosi had settled into a cycle of mad scientist horrors that would see them through till the end of their respective careers. The Invisible Ray of the title does not turn anyone invisible, and also you can see it when dark, but it marks the film out as more science fiction than creepy chiller. Scripted by John Colton (who had written Werewolf of London the previous year) from a story by Howard Higgin and Douglas Hodges, it has an ambivalent attitude to science, where here it can cure the blind, but also turn people into murderers.
That first ten or fifteen minutes are great stuff, with Rukh demonstrating how he has harnessed the power of the Andromeda Galaxy to let us see into the past. These scenes have suitably cosmic scope, with planets and stars seen flying by until we get a glimpse into the past: Earth, thousands of millions of years ago, and an asteroid hitting it somewhere in Africa. This is where Rukh wants to head for, because he knows that a sample of the meteorite will have incredible properties, but unfortunately once he gets there, taking wife and sceptical doctor Felix Benet (Lugosi) among the party, the story turns into a clichéd Darkest Africa adventure, complete with frightened natives and unconvincing jungle sets.
Nevertheless, Rukh finds his meteorite, and with it a new element he names Radium "X". Meanwhile, Diana has found love with the nephew of the expedition's sponsor, Ronald Drake (Frank Lawton), but how can that progress when she's still married to Janos? Love will find a way, because the doctor has been exposed to his element and now not only glows in the dark but can kill to the touch. Lugosi is interesting here as he's playing the good guy, very well too, and Benet concocts a serum that Rukh can use to allay the symptoms, but his mind is being slowly eroded and when they return to Europe he gets it into his head that his work has been stolen by the rest of the party, mainly due to their putting it to better use than he can. And so he embarks on a campaign of murder and the story heads to its tragic conclusion. Nothing beats that opening, but it's certainly eventful; if only Rukh had heeded the advice of his mother and kept away from everyone and concentrated on his experiments. But then we'd have no story, I suppose. Music by Franz Waxman.