As a dust storm descends upon Independence, Abby and Tom find themselves desperate for shelter. Gus has a lead that can potentially help Calian. Kate, Hoyt and Lucia work together, but things do not go according to plan. Kate stumbles upon something very unexpected and leaves her questioning everything.

Through a series of letters Gus writes to his late wife, the origin stories of Abby, Hoyt, Kate, Kai, Calian, and Tom are revealed along with the role each played in each other's destiny.