After Regina crushes the heart of her Dark Half, it appears Storybrooke will finally enjoy an era of tranquility. But this reprieve is short-lived when the Evil Queen reemerges and wreaks a level of havoc and terror that makes her previous cruelties pale by comparison. Desperate to right her counterpart's wrongs, Regina fights the ultimate battle against her nemesis, but can one survive if the other is destroyed? Meanwhile, Gold's attempt to win back Belle before their child is born has heartbreaking consequences; Snow and David face a new, even more insidious curse; and just as Emma begins to envision a happy ending with Hook, she discovers she's destined, as the Savior, to die at the hands of a sword-wielding assassin -- unless she can somehow change her fate.