In an effort to protect Emma, Regina steps up in a surprising way that will test her mettle as a force for good. King Arthur and Queen Guinevere throw a royal ball to welcome the heroes to Camelot, but when the celebration takes a deadly turn, David and Robin must leap into action or lose a crucial asset in the fight to save Emma. Back in Storybrooke, Hook deploys a tried-and-true technique in hopes of bringing Emma back to the light while the heroes discover that some unexpected baggage has followed them home from Camelot.

After receiving a cryptic warning from Lancelot about Arthur's intentions, Mary Margaret realizes Arthur may be the heroes' biggest threat, but when she is unable to convince David of the danger, she takes matters into her own hands. Meanwhile, Hook's unwavering love for Emma provides a glimmer of hope in her struggle against the unrelenting voice of Rumplestiltskin. In a Camelot flashback, Guinevere senses that Arthur is losing his way, consumed by his obsession with making Excalibur whole, so she sets out with Lancelot on her own quest into the heart of darkness. In Storybrooke, Dark Emma unleashes a secret weapon in the next phase of her plan to find the brave soul she needs to draw Excalibur from the stone.

In Camelot, as Mary Margaret and David attempt to retrieve the Dark One dagger, Emma uses a Dreamcatcher to look into the past to see how Merlin was transformed into a tree. Together, Emma and Regina figure out the critical ingredient they must acquire to free Merlin, but it's a race against Arthur, who does not want Merlin released. Meanwhile, with encouragement from his moms, Henry musters up the courage to ask Violet on a date. Back in Storybrooke, the heroes break into Emma's house hoping to locate Gold, but what they find will give them a glimpse of Emma's end game. Far from prying eyes, Merida sets about the mission Emma has tasked her with and begins molding Gold into the hero they need to draw Excalibur.

Regina reels from the death of Robin Hood, and everyone tries to give her room to grieve, but when the heroes discover Gold has stolen Hades’ Olympian Crystal and tethered all of Storybrooke’s magic to it, they set out to stop him. Henry decides he no longer can stand all the pain magic has caused his family, so he goes rogue, with Violet in tow, to destroy magic once and for all. Meanwhile, Zelena, Snow, David, and Hook attempt to open a portal that will return Merida and the other Storybrooke guests to their homes, but things go awry, and the group winds up in a deranged new world.

With the possibility of magic being destroyed and the fate of Storybrooke hanging in the balance, it’s a race for Emma and Regina to track down Henry before Gold can find him first. Regina continues to struggle with her frustrations over her former evil-self and, elsewhere, Snow, David, Hook, and Zelena are imprisoned and must contend with two very disturbed individuals that may give Gold a run for his money.

The Evil Queen and Hyde continue on their quest to steal Dr. Jekyll's serum; Snow looks forward to her first day back as a school teacher; and while Emma looks forward to Hook moving in with her, Hook finds himself trying to protect Belle from Mr. Gold, who has made sure she can't leave the confines of the pirate ship.

Emma and Regina formulate a plan to trap the Evil Queen in a prison of their own making, while Snow and David adjust to life without each other. Meanwhile, Zelena agrees to help Belle, and together they enlist Aladdin to steal a magical object from Mr. Gold that could protect Belle and her unborn child from him forever.

Emma regains her memory but discovers that the Black Fairy has set the perfect trap for her. Meanwhile, the Evil Queen makes the ultimate sacrifice to save her former kingdom, and Gold is forced to choose between Good and Evil.