Being the Dark One means succumbing to the darkness, and as viewers see on Once Upon A Time, being the saviour doesn't keep that darkness at bay.

Emma Swan (Jennifer Morrison), once the hero of Storybrooke, is now the town's biggest villain after becoming the Dark One at the end of last season. However, those who care for her hope there's a way to save her from the darkness that consumes her.

So far, though, no one's made much progress in saving Emma, and with each episode, Emma's heart seems to grow ever darker. Her goal is to pull Excalibur from its stone to kill the light inside of her and let the darkness take over, but why is she so desperate for her plan to work? What is her endgame?

In a sneak peek from the next episode of Once Upon A Time, Mr. Gold (Robert Carlyle), the former Dark One, asks Emma her plan, as well as about her motivations. Instead of answering, Emma stays quiet and summons Merida (Amy Manson), whose heart Emma now controls, to train Mr. Gold to become a hero because only a hero can pull the sword from the stone.

In an interview with Entertainment Weekly, Morrison spoke about the transition of Emma from saviour to Dark One.

"There was always this fight within her to be able to overcome things and try to be a stronger, better person, and now that she has this darkness within her, her instincts are to be selfish, which has never been her instincts as good Emma," said Morrison. "That immediately changes every decision, and it immediately changes the way that she is capable of being manipulative, and conniving, and vindictive. All of those things were things that she was constantly pushing down and not dealing with as good Emma and overcoming and making the good, positive choice. And now, because she has that Darkness fueling her, when she's faced with decisions, unfortunately, the selfishness is what's pushing forward first."

This season has already held many surprises, most specifically uncovering the truth about a Camelot that isn't as lovely as the legends paint it: King Arthur is pretty much a jerk and Guinevere is under a spell that forces her to love the king, rather than her true love, Lancelot. Of course, viewers still don't know why Arthur became that way, but he does possess an obsession with fixing Excalibur, which is missing its tip: that missing tip is actually the Dark One's dagger.

Once Upon A Time airs on ABC on Sundays.

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