OUAT season 5 Dark Swan
Emma becomes Dark Swan in Once Upon A Time season 5 ABC

Once Upon A Time season 5 returns on 27 September on ABC where Emma Swan will turn into the Dark One.

In the season 4 finale Gold finally gets free of the dagger's hold, but darkness tries to take Regina. Emma then sacrifices herself and is whisked away by the dark powers, leaving only the dagger behind with her name etched on it, thereby making her the Dark One.

A TVGuide report has some spoiler details about the OUAT season 5 premiere plot.

"Emma's friends and family, led by Regina, will try to find a way to save her before she becomes the full-on Dark Swan. But this means tracking down the sorcerer Merlin, which brings them to Camelot and the Knights of the Round Table. Brave archery lass Merida (Amy Manson) will join the show as well," said the report.

"This is a mash-up show," co-creator Edward Kitsis said. "This is the show where the Wicked Witch is sisters with the Evil Queen, and they also know Cruella De Vil. So what a bummer if we had King Arthur and he never got to meet Merida."

Also, King Arthur and Charming will bromance while Robin will try to figure out a way to deal with accidentally impregnating his girlfriend Regina's wicked half-sister.

Once Upon a time season 5
Snow, David, Emma, Hook, Regina and Robin in OUAT season 4 finale ABC

Jennifer Morrison and Colin O'Donoghue who play Emma Swan and Hook, dished about Dark Swan and their characters' relationship in season 5.

Morrison explained, "Emotionally, it's interesting because there's something really fun and free about Emma in the darkness. She's just free of the gravity of what other people think, the gravity of worrying about saving people."

"There's lightness in a sense in the darkness because she doesn't have to do the right thing. She doesn't have to try to be the stronger, better person all the time."

"She [Emma] is going to be fighting against the darkness," Morrison teased.

Colin O'Donoghue however teased that for Hook, "nothing is more important to him in this moment than Emma" and added, "He has spent so long fighting the darkness and hating the Dark One, so it's very complicated for him. He's trying to figure out a way to bring her back."