Emma works with Regina to find out who took everyone's memories from the past year, as flashbacks show the Evil Queen and Robin Hood attempt to break into her castle, which has been overtaken by the Wicked Witch.
The residents of Storybrooke try to prevent Zelena from stealing Mary Margeret's newborn baby for use in her evil plan, as flashbacks show Glinda attempt to convince Zelena to fight her evil tendencies and join her as a protector of Oz.
When an icy spell is cast on Marian, the residents of Storybrooke place the blame on Elsa, unaware the mysterious woman who runs the town's ice cream parlor has the same powers as Elsa and is trying to frame her.
Emma becomes determined to discover the Snow Queen's plan after discovering she was once her foster mother and Belle searches for the Snow Queen's hideout, as flashbacks show her travel to Arendelle to discover the fate of her mother.
Emma captures the Snow Queen and interrogates her at the sheriff's station and Regina and Robin's relationship grows increasingly complex, as flashbacks detail information about the Snow Queen's life in Arendelle.
Gold interferes with the Snow Queen's plans for his own agenda, as flashbacks show the Snow Queen try to pit Elsa and Anna against each other. Emma turns to Gold for help getting her powers under control.
As the Spell of Shattered Sight approaches Storybrooke, Emma and Elsa search for Anna, Belle and the fairies work on an antidote, and Gold, with a reluctant Hook as his servant, works on an exit strategy.
In the aftermath of the Snow Queen's curse; Emma looks for a portal so Elsa, Anna and Kristoff can return to Arendelle, Regina makes a difficult choice, and Gold's quest for power reaches a dramatic conclusion.