A society of human-like beings called tetrapeds dwell under the ocean floor in a dystopian but sophisticated society with a caste system. Claiming to know what's good for the country of Pelagia, the government is an alliance of corporations who tolerate no dissent. When a group of citizens concerned about their polluted environment is deemed treasonous, they are targeted for elimination. Landley, a member of the lower caste is among the targeted after her cavemate is murdered. Her heartthrob detective discovers the plan and informs the professor who leads the group. They discover and escape to a legendary Lost Sea where the story begins.
The reader will be kept in suspense as the group struggles with the challenges of surviving in a primitive environment, living in fear of the likely discovery of their location, dissent among their ranks, and an encounter with an existing advanced society in the Lost Sea, which may or may not be accommodating to them. Their allies who remained in Pelagia risk their lives by delivering supplies and keeping their ears tuned to hints that the new CEO might decide to drill to search for the Lost Sea. The pristine nature of the environment in which the colonists live fails to compensate for the constant tension about their future.