Penny Grace successfully traveled through time, outsmarted a paradox, and survived countless historical tragedies. Now, she must face her biggest challenge yet: stopping The Shadow once and for all. After terrorizing the dark world for eons, The Shadow now wants control over Earth. Unless Penny surrenders her past heroics, all life on Earth will die of thirst while the dark world drowns. But giving up would mean turning her back on everything Penny's fought to protect, and she's more determined than ever to save both worlds from The Shadow's tyranny.

Penny and her nemesis Kyle team up to unravel The Shadow's rage toward humans in hope that understanding the past can help them protect the future. As Penny and Kyle work together, Kyle opens up about his past and Penny starts to see the mysterious man less like an enemy and more like a brother. But does that mean Kyle has changed? Is he trustworthy? Or is his new vulnerability a tactic to manipulate Penny even more?

When Penny realizes the only way to stop The Shadow is to trap them both in a paradox, she needs the help of those she left behind to pull it off. But returning home to Cheyenne means facing the consequences of her choices. If Penny wants to save multiple worlds, she needs to convince the family that forgot her and the ex-boyfriend she still loves to help her make the ultimate sacrifice.