Hook being released from the Dark One Vault, where the darkness is contained, is featured in the forest.
Three weeks earlier in Camelot, Emma has a box with the spark of fire in it and she tells Henry she has it and can reunite the sword. He says they're not back with him then says Merlin is missing too. Granny and Henry are frozen with magic by Merlin, who is there and he's following orders by Arthur. He says Arthur tethered him to Excalibur and has ordered him to unite the sword. She refuses and he says Arthur has her family and will kill them unless she hands over the dagger and the flame. Emma says it's not a flame yet, just a spark. Emma says she can't give up without a fight. Merlin begs her not to seek vengeance and not make the same mistakes as Nimue.
Emma tries to raise the spark to a flame when Rumplestiltskin's manifestation is there and says Arthur will kill her if he reunites Excalibur but she says she has no choice and can't risk the lives of her family. Rumple says she can only light it when she's ready to reject darkness. Henry finds Emma talking to herself and he asks what she's doing and what the voices said. She says they told her she wasn't ready to give up the darkness. He shows her a photo of a house that he and Hook were looking at for their Operation Light Swan. Emma shuts the lid on the spark and says she has to use the darkness again, so she goes to the woods and sees Arthur has her family tied to trees. She tells him to free them but Arthur wants Emma to hand over the dagger and spark or he'll unleash Merlin, and brought along Zelena to make sure she complies, asking if she should kill Hook or David first. Emma hands Zelena the spark but when she opens it Zelena discovers its a spell that traps her against a tree. Furious that Emma tricked him, Arthur orders Merlin to fight her and they do battle by using magic. Merlin says he wishes Emma could defeat him, but Merlin knocks her back. Arthur, believing he has the upper hand, orders Merlin to kill Mary Margaret by choking her with the tree's vines. Emma then pleads with Merlin to fight back against Arthur telling him that he is the greatest sorcerer of all time and if he can't fight off the darkness, no one can. It works and stops the vines from choking Mary Margaret.
Arthur continues to force Merlin, who is pushed to the limit, but the distraction gives Hook time to free himself and comes at Arthur but taking the sword and Arthur runs off and releases Zelena as the two disappeared. Emma thanks Hook and heals a cut on his neck. He says now they have the sword then grabs it so they just need to light the spark and they can get the darkness out. Back at Granny's Hook recounts the adventure to Henry who is excited. David and Regina report back that Arthur is far away and Emma is outside with the spark trying to make it work. Regina comes out and she tells her that Rumple is playing with her telling her she can't light it because she's not ready to give up the darkness, even if she is lured to it if it's wrong. Regina grabs the dagger and commands her to tell her why she's afraid to give up the darkness, knowing she can't protect her family if she does. Regina says that's not the truth and uses the dagger to test her. Hook, David and Mary Margaret come up and Hook snatches the dagger from Regina, who tells them she wasn't being cruel, she was helping her find the truth, even though it's painful.
Hook tells Emma he's sorry that Regina used the dagger on her but Emma says Regina was right and she shows him the ad for the house. She says she's afraid of the future. He asks if she's scared to move in with him and she says it's everything. She says she's afraid because she does want a future with him and the minute the darkness is gone, the future begins. He says that's music to his pirate ears. He says don't be afraid of the future and kisses her. Hook says he's just happy to know that she has one and he goes limp. Emma says that's not enough for her. She holds him and cries and then takes Excalibur and floods it with magic. In the diner, Merlin tells them it's too late and he begins to sprout dark tendrils. These spread to the sword Emma has and gold magic flows over Killian and he's gone then his name appears on the handle of Excalibur. Then in a flash, Emma is dark as she is now white hair and all. A flood of blackness forms and Killian is transformed.
In the woods, David, Hook and Robin are ready to confront Arthur at his tent, and they brought along weapons just in case. David demands to know why Arthur lied and tried to burn the Crimson Crown, and tells him about a message from Merlin about Nimue. Arthur, however, decided to throw the threesome off with a table, then escapes into the wood with them in pursuit. After Arthur trips, he sees Hook and kicks him down and draws Hook's sword on him, but just as he was about to kill him, Emma suddenly shows up and uses the now-united Excalibur to send Arthur towards a tree and tells him this sword controls no one now. Hook says thank you but Emma warns him not to. He also apologized for what he said on his ship, and asks if he means about not loving her believing that she's still herself and she asks what he wants. He says he wants her help and asks who Nimue is. She says this will all be over tomorrow and Nimue doesn't matter. He asks why she needs the sword. Emma walks away and Hook says he knows she has reasons for doing this, but Emma tells Hook she's doing all of this for him, then disappears. Arthur is in a cell and Hook wants to know who Nimue is and what he's hiding, but Emma took his memories. Hook says Emma told them this was about him but Regina says Emma is manipulating him as Regina and Mary Margaret are convinced that Emma is gone. Hook believes Emma hasn't used the sword yet, but Regina thinks Emma still needs another ingredient for a spell. Hook is determined to find out what went on in Camelot and visits Gold at his shop when Hook comes in and Gold tells Belle to put down the crossbow. He says he had some squid ink set aside but the new Dark One took it. Hook says Dark Ones are clever then asks what's going on inside Emma's head. He tells Gold what Emma said about it being about him. Gold says he recognizes the look on her face – regret. He says he went dark to save his son. He says he convinced himself everything was for that but things did not work out. He tells Hook to find out what Emma is atoning for to get the answers. Hook says he can't find her then Gold says give her a reason to find you. Hook goes outside and calls for her and asks what happened between them. He asks what the hell she wants.
Hook goes calling for Emma and stands on a rooftop to get attention. He jumps off and she catches him then asks why he was so sure she'd save him. He says he was optimistic then asks what happened between them in Camelot. He says he forgives her and she says she doesn't need that. He says there's nothing she's done as bad as what he's done. He shows her a ring that belonged to Barnaby and he killed him in front of his wife. He says every ring he wears is a sad story. She shows him the ring he gave her to keep safe and he says it belonged to his brother Liam. She tries to give it back but he says keep it. He says he wore rings as trophies and now they're just reminders. He says he loves her no matter what and she says she needs to show him something. She takes him to her house and she points him to a telescope. He looks and sees the sea and a full moon of waves. She says he told her the ocean calmed him and he says it's a nice home but she says he picked it, not her. He looks at the newspaper and says it's his handwriting. She says he told her this was their future and she says everything she did was to keep that future alive. He asks again for the truth and she says they're almost there and kisses him. She says she can't tell him everything because he would try and stop her. He passes out after the kiss and as he gets groggy he asks what she's doing.
At the hospital Zelena reading "Hansel and Gretel" to her unborn child, then goes in pain, screaming and banging on the door. Regina and Robin show up and they look at her pregnant body, which has accelerated by seven months (from two months), a result of Emma's dark magic. Zelena says Emma did this with her onion rings. Dr. Whale is there and Zelena says get this angry baby back, and Whale reminds her about the last baby he delivered she tried to steal. Regina asks why his hair is blond, saying it was Emma's doing. Belle and Mary Margaret run in and tell them that Emma is coming for the baby and needs the cries of a newborn child. Zelena begs Regina to take off the cuff but Regina says no. Zelena immediately delivers a baby girl, as Regina and Mary Margaret wait in the hall and Mary asks if she's ready to meet her new family but she says she doesn't know. As Robin hold the newborn, Emma is there but she wants Zelena instead, and disappears with her after throwing Whale against the wall yet again.
Zelena and Hook are both chained to the wall in Emma's basement, as Zelena thinks Emma is casting a spell to take her magic. Emma says she's giving her dark magic to Zelena. Hook asks why keep it a secret and she says she won't let him stop her. She says the dark magic must be put into a vessel then Emma will cut her down. Emma says that's why she needed the baby out. She reminds him that Zelena killed Marian and Neal. Hook says it's murder. Hook says they can talk to Merlin but she says he can't help them anymore. Hook asks again why she's really doing this. Mary asks David and Regina how Emma can use Zelena to end dark magic. Regina says no one hurts her sister but her and tells them she's going to show Emma how dark magic really works. Zelena says the anti-magic cuff is the real problem. Hook says he has magic in his hook. He says the last time he helped her, she betrayed him. She says he has no choice now. He cut off the cuff and she gets rid of the shackles then puts herself into a fresh outfit and then comes over to Hook and undoes his shackles. Mary Margaret and David argue with Regina over going to war with Emma. Regina says Emma gave her the dagger because they knew she was the only one who could act. Emma comes out and says when she's done with Zelena, they will all be better off, saying she knows Regina will be happier when Zelena is gone. Emma puts up a magic barrier around the house. Zelena tells Hook they have to sneak out the back but Hook says he's not going. He says he needs to stop her. Hook searches her house then takes a painting off the wall but then Emma comes in and he squirts her with squid ink and says she's a villain now like Regina said. He says she has to tell him what happened in Camelot. Zelena is there and says she will make the Dark One pay. Zelena stabs Hook in the chest and he asks what's happening. She says she found the Dreamcatcher outside and Emma whispers not to trust her then says she can explain everything. Hook says do it and she shows him his memories. It turns out she used the dark magic to save Hook and holds him and cries, then takes Excalibur and floods it with magic. In the diner, Merlin tells them it's too late and he begins to sprout dark tendrils spreading to the sword and flows over Killian and he's gone then his name appears on the handle of Excalibur resulting in Emma's transformation. Hook is turned into the Dark One. Emma tells him she's sorry and says she had no choice. Hook says there must be another explanation. Zelena hands Hook the sword and she removes a spell and shows him that his name is on the sword part and Emma's name is on the dagger end. Emma says she wanted to make up for this and says it was the only way to get rid of the darkness in both of them. She says all she's done is try and save him but Hook is angry and says they have no future. Zelena asks if he's ready to find out what else happened in Camelot and he says yes but first they have to take care of Emma.