A scientist, angry at being scoffed at by the Naturalists' Society, decides to experiment with a drug that turns animals into their prehistoric counterparts on himself. After turning his cat into a saber-toothed tiger, he turns into a Neanderthal man and goes on a killing spree.
This SF/Horror film is pretty bad; it's overlong, overwritten, and incredibly talky. There are scenes where characters talk endlessly about other scenes that you've already seen. Robert Shayne also plays the rudest scientist I've ever seen; I suspect that the Naturalists' Society threw him out not because of his theories, but because he insulted them with every other sentence he'd deliver. This is definitely not a high point in fantastic cinema. Beverly Garland is also on hand in this one, but she's given little to do.