A young woman is about to learn something unique about herself. She is not from this Earth. When she was a baby, she managed to give her parents the slip just long enough to get thoroughly lost. She stumbled upon a dimensional distortion and was somehow transported to one of Earth's other possible permutations.
Now, on her seventeenth birthday, the energy keeping her anchored in a dimension that is not her own has finally weakened enough that it can no longer keep her there. The day after her birthday party, she once again wakes up in a strange place with no memory of how she came to be there, only now she is back where she belongs. The problem is, on her earth, there are no people or laws to protect her. She finds herself on an Earth where just about everything either wants to defile her supple young body, or eat her.
Now she must find a way to survive in her new surroundings, lest she become a monstrous spider's next meal, or a despotic chieftan's favorite new love slave.