The Isle of Man now rests on the bottom of the Irish Sea, cut off from the surface world and surrounded by the dark waters of the unknown. While Mannix, their young savior, provides the inhabitants shelter and life through his unique blue energy, Imogen “Genny” Creer uses her unparalleled intelligence to guide the Keepers, the protectors of the island, and prevent their society from falling into disarray.

Despite being married to the man she loves, managing the Keepers’ science division, and being seven months pregnant, Genny is far from content. She is deeply disturbed by the secrets still kept from her by her fellow Keepers. A counter-group called Free Atlantis is gaining ground, and Genny finds that she agrees with their precepts. Surely man is not meant to live underwater. Motivated by a laser-focused quest for knowledge and a baby on the way, Genny is determined to find a way to restore Mannin to the surface, despite the Keepers fighting to keep Mannin underwater.