After Mr. Gold's house is robbed, Emma keeps a close eye on him when it looks like he wants to track down the criminal and dole out some vigilante justice as payback, and Valentine's Day finds Mary Margaret, Ruby and Ashley having a girls' night out. Meanwhile, in the fairytale land that was, Belle agrees to a fateful deal to give up her freedom in order to save her town from the horrors of the Ogre war.

Emma and Regina team together in order to find a way to save Henry's life. Meanwhile, in the fairytale land that was, Prince Charming attempts to escape from the Evil Queen's clutches in order to reunite with Snow White who, unbeknownst to him, has already taken a bite of the Queen's poison apple.

Cora brings the giant to Storybrooke, where he unleashes vengeance on the town; Emma and Henry go with Mr. Gold to search for his son; Greg asks Belle what she saw on the night of his accident; Anton the Giant befriends humans.

Mr. Gold asks David for help jogging Belle's memory; Anton's magic beans begin to grow; Rumpelstiltskin goes after a thief.

Emma returns to Storybrooke to reunite Lily with Maleficent while Regina and Robin struggle to cope with the implications of Zelena's pregnancy. When Gold's health takes a turn for the worse, Isaac looks to a new ally for help procuring the magic ink he needs to re-write history. In a Fairy Tale Land flashback, Cora returns from Wonderland to beg Regina's forgiveness on the anniversary of Daniel's murder. Cora vows to help her daughter find true love, but Regina remains suspicious of her mother's intentions.

Immediately after becoming the Dark One, Emma disappears and the heroes must band together to save her, but first they have to find her, which will require the help of an unlikely ally. Meanwhile, in the Enchanted Forest, Emma struggles to resist her dark urges as she searches for Merlin in the hope that he can stop her transformation. Along the way to Camelot, she gets help from the plucky and brave warrior princess Merida, as well as King Arthur and his Knights of the Round Table.

In a Camelot flashback, a chance encounter with Merlin, David, Hook and Belle gives Merida new hope in her quest to save her brothers from the usurping clans of DunBroch. Unwilling to leave anything up to fate, Merida brings Belle along on a dangerous journey that culminates with an invaluable lesson in bravery. In Storybrooke, Regina, Mary Margaret and David discover the spell that would allow one of Merlin’s chosen to communicate with him, but when Arthur fails to reach the missing sorcerer the heroes grow suspicious. Meanwhile, Emma commands Merida to kill Belle in hopes of forcing Mr. Gold’s heroic transformation. With Merida unable to disobey Emma’s orders.

Tensions in Camelot come to a head when Merlin, now under Arthur’s control, delivers an ultimatum to Emma: hand over the Dark One dagger and the Promethean spark or he will kill her entire family. Refusing to give in, Emma and our heroes face off against Arthur, Merlin and Zelena in an epic battle of magic and will. Just when the end is in sight, Emma is forced to make a gut-wrenching choice that no one saw coming. Back in Storybrooke, Zelena’s pregnancy mysteriously accelerates and Hook goes to new and desperate lengths to get answers from the Dark Swan.

In a Camelot flashback, Hook becomes a Dark One and his lust for revenge against Rumplestiltskin is reignited. When Emma and Hook disagree about their best course of action, the final pieces of the puzzle are revealed as events in Camelot catch up to the present and we witness a charged confrontation between the forces of light and dark that sends our heroes on a collision course with destiny. Meanwhile, in Storybrooke, Hook’s centuries old lust for revenge against Gold puts both of their fates in jeopardy while Emma’s love faces the ultimate test as she tries to convince Hook to turn away from the darkness before she, Mary Margaret, David and Regina embark on a new mission as an unsuspected evil is released.

As Storybrooke continues to welcome the new arrivals from the Land of Untold Stories, families, friends and enemies are reunited once again. When Cinderella searches for her step-family, intent on settling their unfinished business, Emma, Hook and Henry scramble to help her before it's too late. Meanwhile, Regina attempts to bribe Mr. Hyde for information about how to defeat the Evil Queen, and Snow helps Dr. Jekyll find a laboratory for his work.

Gold and Belle convince Emma to help Gideon, explaining that together they can stop the Black Fairy. Henry experiences a disorienting shift in his powers that forces Regina to seek counsel from the previous Author. Meanwhile, in Fairy Tale Land, Hook attempts to win the assistance of an old adversary by betting his most prized possession on a game of cards. And, in a flashback, the Black Fairy tortures young Gideon in hopes of molding him into the perfect apprentice.

Henry wakes up in a strangely changed Storybrooke where Emma is a mental patient and the rest of his family has disappeared.