Rewind (Replica: The Plague Trilogy I)

No one can identify the cause of the mysterious disease. There’s evidence that the bacteria infected human genes as much as a million years ago. Back in the prehistoric age. Back when dinosaurs roamed the land. Back when cavepeople communicated in grunts and gestures. And the bacteria has been dormant—until now.
Amy’s refined genes make her immune to this terrible plague. But when someone close to her shows symptoms of the disease, Amy will do anything to help find a cure. The only way: traveling back to the time when it all began . . .