Sam's ability to leap back and forth between time has been both a blessing and a curse. On one hand, he can use his abilities to help the police solve the most heinous crimes, but on the other, he can't ever intervene in what he witnesses. He knows doing so could altar the present in horrific ways. But when a woman, Elizabeth, from his childhood comes begging for his help in finding her sister's murderer, Sam's own demons make him break this golden rule. It's a rule for a reason.