The third novel in the Lucky Starr series, six juvenile science fiction novels by Isaac Asimov that originally appeared under the pseudonym Paul French.

Shortly after returning from the Asteroid Belt, David "Lucky" Starr learns that his Science Academy roommate Lou Evans had been sent to investigate trouble on Venus, but the Council of Science office on Venus has requested that he be recalled and investigated for corruption. As Starr and John "Bigman" Jones are shuttled to Venus, their pilots suffer an episode of paralysis, and Starr is required to keep their craft from smashing itself against the surface of the Venusian ocean. Afterwards, the pilots have no memory of the event.

Upon reaching the Venusian city of Aphrodite, Starr and Bigman meet Dr. Mel Morriss, head of the Council of Science on Venus, who explains that Venusian scientists are perfecting strains of yeast that can be processed into luxury foods for export; whereas for six months there has been a growing series of incidents of bizarre behavior among the human colonists, often followed by amnesia. Morriss believes they are being telepathically controlled by an unknown enemy.