Stel Caine rises from the depths to the sun-blasted surface of the Earth, the first human in millennia to do so. She's closer than ever to discovering the deep-space probe, which holds within it the potential to save all mankind. But eons of radiation have given birth to strange new life, and humans are no longer the dominant species here. Meanwhile, deep below the waves, Stel's daughters start their own journeys topside. Will this family reunion secure the key to humanity's salvation--or snuff out our light forever?