Season 3 B description from ABC
[…] In turn, Regina obliterated her original curse, which erased Storybrooke from existence and whisked its residents back to Fairy Tale Land, leaving Emma and Henry together back in our world with pleasant memories - but with no memories of Storybrooke or its residents, and with Storybrooke itself seemingly gone for good.
And they all lived happily ever after… Hardly!
All is not well back in the Enchanted Forest when Hook comes calling on Emma in New York City in an attempt to jog her memory so that she can once again help her fairy tale family and friends out of a desperate situation. Everyone she holds dear is in danger as a new foe emerges - the Wicked Witch of the West (Rebecca Mader, “Lost”). Hook now must enlist Emma in an epic struggle that spans worlds: with the highest stakes possible - the fate of her family. No one remembers how they were transported back or the past year they had spent back in Fairy Tale Land. But someone in town is responsible for this curse, and all clues point to the Wicked Witch of the West, whose agenda in our world is a mystery. In an attempt to break the curse, new fairytale characters will be revealed and old acquaintances will be revisited. But not everyone can be trusted.