What it is to be human doesn't apply anymore. The surface of the Earth has been poisoned by years of abuse and now most life lives beneath the waves of the ocean. Over the last 500 years, humans have become fragmented and specialized by genetic manipulation, but two main factions exist in the Undersea. The hybrids, a race that continues to genetically modify themselves to climb the social ladder, and the humans, the unmodified organic race that makes up the lowest tier of society.While Jack desperately looks for a way to save Alex, the Sanctuary is rocked by a fiery explosion, scattering the residents and forcing Jack and Lexi into the Undersea. Meanwhile, Alex, being tortured physically and mentally by her husband, ends up pregnant. The clock counts down as Jack runs out of time to save her before she has her child. Once she does, Henry has no reason to keep her alive.