Once Upon A Time returned to answer the question: What has become of Dark Swan? At the end of last season, Emma Swan let the darkness envelope her leaving the rest to deal with the consequences.
Hook picked up the dagger with the name Emma Swan embossed on it. He tried to call Emma to him but she didn’t come and Regina told him it was because she was in another realm.
As the crew in this world tried to find a way to get to Emma, Emma herself was dealing with being back in the Enchanted Forest. She was also shocked to find that Rumpelstiltskin talked to her as like a dark version of Jiminy Cricket. He was kind of her guide into the darkness.
In the other realm, Emma meets up with Merida (from Brave) after Rumpelstiltskin tells Emma a light fairy is needed to help her get rid of the darkness. But Merida is in search of the fairy, too, planning to use it to free her brothers from being kidnapped. Emma teams up with Merida in hopes of using the fairy after Merida is done, but Rumpelstiltskin says it can only be used once and encourages Emma to steal it.
In the “B” story, the viewers see the seeds of the story of King Arthur and his Knights of the Roundtable as they search for Excalibur. When Arthur pulls the sword from the stone, it is only half there; The Dark One’s dagger is at the bottom of Excalibur’s sword.
Meanwhile, the rest of the group struggle to find a way to find Emma. They realize they must use the dark power of Zelena, and Regina begrudgingly agrees. They use the power at Granny’s restaurant to travel to the other realm to find Emma.
When they find Emma, they also run into King Arthur and his men and they are all taken to his castle.
Just as they are walking across the bridge, the time frame jumps ahead and everyone wakes up in Granny’s with their memories wiped again. Just as they are trying to remember what happened, Emma arrives fully emerged as “Dark Swan.”