Regina deals with the repercussions of losing Robin after Emma brings his wife from the past, and turns to an friend for help. Meanwhile, a mysterious ice princess arrives in Storybrooke and unleashes chaos. In the past in the kingdom of Arendelle, Elsa and Anna discover that their parents were killed trying to find a cure for Elsa's condition, and Anna sets out to find the same cure.
Elsa traps Storybrooke within a wall of ice while trying to find Anna, but is unable to release them... and puts Emma's life in danger. Meanwhile, when the power goes out, the townspeople insist that Mary Margaret deal with the crisis. And in the past, Anna visits David and helps him learn how to fight so that he can defeat the dreaded warlord Bo Peep.
Marian falls under a freezing curse and the townspeople believe that Elsa is responsible. When Emma and David go to Robin's camp to look for clues, they find Will Scarlet, who leads them to the culprit. Meanwhile, in the Arendelle of the past, Elsa and Kristoff go to find the urn that Hans plans to use to imprison Elsa, and encounter the Snow Queen.
To prepare for his first real date with Emma, Hook blackmails Gold into restoring his left hand. However, the pawnbroker warns that all magic comes with a price. Meanwhile, Will tries to steal a book from the library. In the Enchanted Forest of the past, Anna has no choice but to agree to do a favor for Rumplestiltskin return for knowledge of why her parents traveled to see the Dark One.
Emma tries to convince a reluctant Regina to help her find the Snow Queen, only to discover that Regina is lying to her about Sidney's whereabouts. Meanwhile, David convinces Mary Margaret to go on a date, but the date turns into a hunt when Will escapes his jail cell. In the past, Emma befriends another young orphan who isn't all that she seems.
While Emma and Regina track down the Snow Queen's ice cream truck and find a clue to her connection to Emma, Belle sets out to right a wrong that she did to Anna long ago... by using Gold's dagger to compel him to help. In the past, Anna agrees to take Belle to Grand Pabbie to restore her memories of what happened to Belle's mother.
Emma and Elsa manage to capture the Snow Queen, unaware that she wants to be captured so that she can play on Emma's self-doubts. Meanwhile, Robin chooses between Regina and Marian, and Henry attempts to learn the secrets of his grandfather's pawnshop. In the past, Ingrid learns of her powers and her sisters Helga and Gerda vow to stand by her no matter what.
Gold manages to imprison the Snow Queen and plans to strip Emma of her light magic for his own purposes. Meanwhile, Robin asks Will to help him find the storybook's author, and Emma grows increasingly frantic as her powers run out of control. In the past, Elsa frees Anna and together they try to trap Ingrid within the urn.
Gold continues with his plan to use the Sorcerer's Hat against Emma so that he can free himself from the Dark One's dagger. Meanwhile, Regina isn't convinced that she will ever find her happy ending, but Mary Margaret convinces her otherwise. In the past, Ingrid turns Anna against Elsa and learns what she must do to obtain her third sister.
The Snow Queen unleashes her spell, and the townspeople try to prepare a cure before sundown. Gold forces Hook to use the Sorcerer's hat to drain the fairies of their power and use it to escape Storybrooke himeslf. Meanwhile, Elsa and Emma try to find Anna, who may hold the cure to the town's survival. In the past, Anna and Kristoff seek out Black Beard to obtain the Wishing Star that will let them free Elsa from the urn.
As Storybrooke descends into chaos as the Snow Queen's spell takes hold, Emma and Elsa try to trick Regina into destroying the ribbons so that they can attack the Queen. In the past, Ingrid adopts Emma and attempts to show the girl that she's a powerful sorceress.
As Emma tries to find a way to get Elsa, Anna, and Kristoff back to Arendelle, Gold uses Hook to prepare the way for his departure from Storybrooke. In the past, the Queens of Darkness abduct Belle to force Rumplestiltskin to give them one of his magical artifacts.
With Gold banished from town, the residents of Storybrooke attempt to resume their normal lives. Hook and Belle search for a way to release the fairies from the Sorcerer's Hat, while Emma, Henry and Regina continue to look for clues that could lead them to the Author. But when a terrifying darkness descends on the town, Emma and Regina are forced to confront the true nature of evil. Meanwhile, in New York, Gold and Ursula enlist Cruella De Vil to join their cause.