Using hypnosis and a dark liquid, the mystic and scientist Oliver Kent sends the superconscious minds of his life-long friends Donald and Joane Cromwell back to the Pleistocene where they inhabit prehuman existences of themselves and discover the origin of Joane’s present-day unease. The Brontosaurus who makes an appearance is out of place in the Pleistocene, but never mind.

Joane Cromwell was the maiden name of Skidmore’s wife, and her name shows up as a character in several of Skidmore’s stories, although not as the same character. However, Oliver Kent does show up in a later story, “The First Flight,” where he once again sends a friend into a previous incarnation.

Mystical Professor Oliver Kent, who first appeared in “The Beetle in the Amber,” is at it again. This time he gives pilot Donald Calvert a globule of concentrated liquid with the advice that drinking it may be a life-saver if he runs into inexplicable physiological changes during his high-speed round-the-world flight. Indeed, the changes happen, Donald swallows the globule, and he finds himself in the body of his prehistoric ancestor, Dowb, who undertakes a similarly difficult flight of his own on the back of a Pterodactyl.