One day a woman steps through a portal and emerges with no memory of where she came from. Taking the name Sadie, she tries to build a normal life, but the peace does not last. When a strange and sinister woman catches up with her, Sadie is forced to run in order to protect the people she has come to love.

Eventually cornered by her pursuer, she must begin the search for the portal once more before an ancient evil reaches Earth. But when the truth of her past is finally revealed, Sadie faces an impossible choice. If she returns home, she may save Earth. If she does not, her enemies may destroy everything she has left. And if she does go back, her own world may be doomed instead.