While everyone in Storybrooke is searching for Merlin and Merida is still trying to make Rumple brave, the flashback dealt with Merida herself. Remember, when fans first met Merida she was trying to save her brothers.
In the flashback to Camelot, Merida is freed from her prison and she goes on to kidnap Belle. Merida believes Belle can help her with a spell to rescue her brothers. In this mini exposition on Merida’s character, the audience learns Merida lost the favor of the clans after she failed to save her father, King Fergus. In a battle, an opposing force’s knight was charging on King Fergus, and Merida drew her bow to save him but her aim was not true and she missed.
Merida gets Belle to do a spell to find her brothers and sees the other clans have them marked for death. She talks Belle into creating a potion that Belle later learns will turn Merida into a bear. Belle talks Merida out of taking the potion, saying the best way to show the other clans she can lead is with her bow.
Merida and Belle arrive just as her brothers are about to be executed with arrows. Merida knocks her arrow in her bow and shoots each of the arrows aimed at her brother, away with just one of her arrows. Showing her prowess forces the other clan members to relent and bow to her.
In Storybrooke, Rumple has escaped and Merida is in search of him – remember Emma has Merida’s heart and the knowledge of the fate of her brothers. After Rumple tracks down Belle, they both make it to his shop where Merida finds them. They escape and Rumple tries to persuade Belle to leave Storybrooke. Belle is horrified by this, saying she can’t leave their friends, and exits the car as Rumple drives away.
Merida catches up with Belle and drinks the potion Belle had made, turning her into a bear. She goes after Belle but Rumple arrives and faces the bear and his fears. He tosses a potion in the bear’s mouth turning Merida into a human again.
Rumple’s bravery is the catalyst for allowing him to pull Excalibur from the stone. He, Belle, and Merida strike a deal which includes Merida getting her heart back. Emma agrees to give Merida back her heart and informs her that brothers are safe. Rumple pulls the sword from the stone and tosses it at Emma’s feet.
Meanwhile, Regina, David, Hook and Mary Margaret are trying to contact Merlin. They try and enlist King Arthur since he was a vessel to talk to Merlin before. They give King Arthur the magic mushroom to use in the potion. leaving him to contact Merlin. They are all perplexed when Arthur says it didn’t work until David finds the semi-charred remains of the mushroom. knowing Arthur betrayed them.
They have one last hop,e realizing Henry, as the author, also has a tie to Merlin. Henry is able to contact Merlin which basically leaves a voice message saying the circumstances are dire and the “dark one” has found him. And adds they need to find someone named Nimue.
Bonus information: The interplay between Dark Emma and Zelena when Emma tries to ally Zelena to her side. Great comment from Zelena that the difference between them is that she doesn’t mind being alone.