After her banishment from the underground city of Arcadia, Ro has found a new home and friends. Gray, the young recluse who saved her, has left with no explanation, and she has put aside her feelings for him to make a place for herself in her new home. When Gray suddenly returns to tell everyone of a threat that may destroy them all, she and Gray go on a dangerous journey to warn others, but a terrible discovery about Gray's past just may tear them apart.