An attempt to greatly speed up evolution proves fatal for its developer, Dr. Benton. His colleague Dr. Janus proceeds with the experiment, this time hoping to use matter from the "cradle of life" deep beneath the sea - the place where evolution began. The area is geologically unstable, a "graveyard" for submarines. But Seaview manages to retrieve a quantity of the material regardless. Then Dr. Janus accelerates it, and the problems really begin: Seaview is suddenly trapped with an unreliable crew and a large - and rapidly growing larger - new lifeform aboard.