Sisters, Doris and Thea, exist worlds apart, despite living within a few miles of one another. Doris with her regular home and regular husband and regular job, and Thea slinking along the edges of society, solitary and invisible. When a storm of biblical proportions strikes, the wayward sisters are begrudgingly forced together as the rain waters rise, each attempting to survive both the flood and each other.

One year later, Thea--now calling herself Sestra--floats throughout a ravaged, flood soaked world. Her former life drowned beneath metric tons of water, she and her only companion, Robert, battle starvation, heatstroke, and the monstrous creatures called Posies that appeared alongside the flood. When they run across what they assume to be an abandoned tugboat, their journey takes a new turn, and the truth about the flood and the monsters seems more intricately linked to Thea's past then she may realize.