Emma Swan made the ultimate sacrafice by becoming the new Dark One, leaving the residents of Storybrooke without their saviour, now the heroes must band together to find a way to save her.
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.
Once Upon a Time stars Ginnifer Goodwin as Snow White/Mary Margaret, Jennifer Morrison as Emma Swan, Lana Parrilla as the Evil Queen/Regina, Josh Dallas as Prince Charming/David, Emilie de Ravin as Belle, Colin O'Donoghue as Hook, Jared S. Gilmore as Henry Mills, Sean Maguire as Robin Hood, Rebecca Mader as the Wicked Witch/Zelena and Robert Carlyle as Rumplestiltskin/Mr. Gold.
Guest stars this season include Lee Arenberg as Leroy/Grumpy, Beverley Elliott as Granny, Amy Manson as Merida, Keegan Connor Tracy as the Blue Fairy/Mother Superior, David-Paul Grove as Doc, Gabe Khouth as Sneezy, Faustino Di Bauda as Sleepy, Jeffrey Kaiser as Dopey, Michael Coleman as Happy, Mig Macario as Bashful, Sinqua Walls as Lancelot, Raphael Alejandro as Roland, Timothy Webber as the Apprentice, Ingrid Torrance as Severe Nurse, Liam Garrigan as King Arthur, Andrew Jenkins as Sir Percival, Lee Majdoub as Sir Kay, Brent Stait as the Peddler, Elliot Knight as the Usher and Mckenna Grace as Young Emma.
Executive producers are Edward Kitsis, Adam Horowitz, Steve Pearlman and David H. Goodman. The series is produced by ABC Studios.