Emma finds a sword embedded in a stone which she is incapable of pulling out without paying a high price in return.
Merlin's Tree is featured in the forest.
The Storybrooke residents are welcomed with open arms in Camelot, and King Arthur and Queen Guinevere announce that they will throw a ball for their guests. In the meantime, they find that Merlin has been imprisoned in a tree, and the only person who can free him, according to Merlin’s prophecy, is the Savior. However, the Storybrooke transplants worry that Emma will become darker if she uses her magic, so Regina lies to King Arthur and says that she is the true Savior. Regina and Emma search Merlin’s tower for clues, but come up empty and are running out of time as the evening's ball is approaching. Prior the dance, Percival visits Regina and woos her with a necklace to wear and she puts it on, but later decides that she cannot go to the ball, claiming that she needs to continue her research to free Merlin. When she later admits that she does not know how to dance, Mary Margaret helps her find a suitable gown while David teaches her how to dance.
That evening at the ball, everyone makes their grand entrances and the couples dance. Henry has developed a crush on a girl named Violet and, after encouragement from David, introduces himself and shares his iPod Nano with Violet. Leroy is able to convince Belle to stop worrying about Rumplestiltskin and gets her to join the dance. However, the event is about to end early when Percival reveals that he had witnessed Regina slaughter his entire family as a child, and knows that she is the Evil Queen and not the Savior, a fact he confirmed earlier by observing her through the enchanted necklace. He tries to kill her, but Robin steps in and fights him, only to be stabbed in the process before David kills Percival. Regina is desperate to save Robin, but her magic does not work due to an enchantment spell placed on Percival’s sword. This prompts Regina to ask Emma to help save Robin by using her magic, but Hook does not want Emma to trigger her dark side. Meanwhile, King Aurthur does not blame them for Percival's death, and admits that he suspected Regina's identity, but still believes she is the Savior. He later confesses to Guinevere that he thinks that there is something suspicious about the new arrivals, but he has to trust them, as they are his only hope of freeing Merlin and finding the missing piece of Excalibur. Emma eventually decides to help Regina despite the risk, but the magic triggers her vision of Rumplestiltskin, who warns her that a price has to be paid if she saves Robin’s life. Emma ignores the manifestation and uses her magic to save Robin, but in the process it triggers the darkness in her, as forewarned by Hook.
The new curse has the residents becoming more fearful of Emma, and the Dwarfs attempt to escape the town; Dopey steps over the town line and is immediately turned into a tree. Back in town, Hook asks Belle for advice on how to deal with loving Emma, who is now the Dark One. Belle tells Hook, "It’s far easier to hate the Dark One than it is to love one." At the marina, Henry summons Emma and apologizes for whatever happened in Camelot. Regina finds them, tells Henry to get far away from Emma, then tries to convince her that she could save Storybrooke; Emma strongly disagrees.
The residents of Storybrooke discover that Arthur and the Camelot empire has been transported back with them, and David admits to Arthur that Emma had been the Dark One all along. While Robin is working in the woods, helping the displaced Arthurians, he is grabbed by a ghostly, winged entity and taken away.
Meanwhile, a lonely Hook summons Emma because he loves her too much to stay away. Emma brings Hook to her new house, where he notices a locked door. Emma then attempts to seduce Hook; when true love’s kiss fails to break the darkness, he rejects her. Emma is mad that he cannot accept her for who she is now, and he equally angry at her for keeping what happened at Camelot a secret.
Belle has learned that the monster that took Robin is a Fury. Someone had used magic in Camelot to save Robin and did not pay the price, which is a life, and the monster has arrived to collect Robin as payment. It will return to the underworld when the moon reaches its zenith, but can be stopped if someone gave their life in his place. Regina confronts Emma, believing that she had summoned the Fury, but Emma reveals that Regina actually did it. That night near the pond, the Fury begins its descent to pull Robin to the underworld, and Charon the boatman appears as its power reaches its zenith. Regina sacrifices herself for Robin, and is joined by Mary Margaret, David, Leroy and Arthur. As all five band together, they successfully pull Robin from the Fury, who disappears back into the underworld with Charon. While everyone celebrates this latest victory, a worried Mary Margaret notes that if they win, Emma loses. At her house, Emma opens the locked door and goes downstairs, revealing the stone with the sword Excalibur in it. Rumplestiltskin, the manifestation of her darkness, says she can make it whole again and use it to suck out all the light forever. Emma tries to pull the sword from the stone but fails, and learns that in order to complete the task, she will have to pay the price, and it will cost someone dearly.
- Robin could not have been wounded from tackling Percivel. He VERY CLEARLY made contact with him BEFORE he could get impaled.
- Dark One magic is very costly by nature. Despite a normal witch or wizard being able to heal Robin's wound without a price, the darkness is different.
- Henry summons Emma by saying her name three times, similar to Beetlejuice.
- Ginnifer Goodwin as Mary Margaret Blanchard
- Jennifer Morrison as Emma Swan
- Lana Parrilla as Regina Mills
- Josh Dallas as David Nolan
- Emilie de Ravin as Belle French
- Colin O'Donoghue as Hook
- Jared S. Gilmore as Henry Mills
- Rebecca Mader as Zelena
- Sean Maguire as Robin Hood
- Robert Carlyle as Rumplestiltskin/Mr. Gold
- Lee Arenberg as Leroy
- Beverley Elliott as Granny
- Liam Garrigan as King Arthur
- Andrew Jenkins as Percival
- Joana Metrass as Guinevere
- Donald Adams as Footman
- Raphael Alejandro as Roland
- Michael Coleman as Happy
- Faustino Di Bauda as Walter
- Olivia Steele Falconer as Violet
- David-Paul Grove as Doc
- Jeffrey Kaiser as Dopey
- Gabe Khouth as Mr. Clark
- Mig Macario as Bashful
- Unknown baby as Prince Neal