Cain, now cursed by immortality, learns that Noah and Evelyn are among those who possess the key to return to Earth. He begins hunting them through their first lifetime, which resembles the western frontier.

A turbulent end to their second lifetime, propels the twins into their final lifetime, a dystopian wasteland. Evelyn and Noah become desperate to reach Siena and Warrick, but an Ancient stranger, Kroden, emerges.