Bioengineering major Aurora Cole and her best friend Luna Lynn accidentally travel to a post-apocalyptic Base where women are scarce. Because their bodies are unaffected by the apocalyptic environment, they are deemed 'optimal reproductive vessels' and are swept into the Base's mandatory Breeding Assignment program. Aurora Cole remains wary of the price behind this 'special treatment' and is determined to find a way back to her original world. Luna Lynn, however, gradually succumbs to the comfortable life and protection, developing feelings for her Breeding Assignment partner, Mason Shaw. Under the surveillance and coercion of the cold Security Officer Ethan Grant, the paranoid Cody Chase, and other Designated Partners, Aurora Cole endures imprisonment, hunger strikes, and escapes, using her wits to get closer to a time machine left from before the apocalypse. After Luna Lynn becomes pregnant, the two friends diverge on the decision to return. Ultimately, Luna Lynn stays in the post-apocalyptic world to protect her child, while Aurora Cole successfully returns home. Five years later, Aurora Cole discovers a hidden causal link in spacetime and resolves to eliminate the source of the apocalypse in advance, bringing salvation to her best friend and the world.
