Hook and Rumple discuss the outcome of their duel, while Hook threatens Rumple with the fact that Belle left him. Everyone else in Storybrooke is trying to figure out what to do. Emma advises they split up to find Hook. Regina and Robin run into Zelena, who wants to discuss their custody arrangement. She wants to raise the baby herself, but Robin and Regina do not support that. But that fight is interrupted by the fact that there are Dark Ones marking them. Rumple arrives and tells them that in order for the Dark Ones to stay permanently they have to trade souls with a living soul.
Regina finds Hook and tries to talk him out of his plan. He threatens her with reminders of who she will meet in the Underworld. Regina tries to remind him that he’s a different man than the one she recruited years ago to kill her mother.
During a storm, Hook is traveling with his brother and father on a pirate ship. Hook wakes up scared and his father comes in and reassures him. But when he wakes the next morning, he finds his father has abandoned him and sold him in exchange for a boat.
Regina and Hook make a deal: He kills her mother if she will send him to a land without magic so he can get his revenge on Rumple. Regina takes him to a tavern where he sees his father working. Hook reveals himself to his father. His father apologizes for leaving him. After he had left them he was caught and saved by true love’s kiss. He married a woman who changed his ways and is a better man, but then she died. Hook changes his mind after hearing this and admits his intention to kill him, but he decides to spare his life. His father asks him to take his young son with him.
Hook went to his father’s house and overhears his father talking to his new son, telling him the same story he told Hook. To make matters worse, Hook finds out he named his new brother Liam. Hook calls him out for what he did and refuses to believe he has changed and then kills him.
Henry is trying to find a way to remove the mark, but Snow has accepted her fate. Emma refuses to give up on her family. She comes up with a plan with Regina. She is going to channel all the Dark One powers into herself and then kill herself with Excalibur to save everyone.
Rumple gives Belle a potion that will keep her safe when she crosses the town line. They share a kiss before she leaves. Regina and Emma show up and Emma asks for Excalibur. Hook gives it to her. Rumple warns Emma that her plan might not work, but Emma is going to try anyways.
Regina and Robin return to her home where Zelena is. She is thinking about baby names and is trying to figure out how awesome her life will be when they are dead. Regina is now worthy of the wand so she uses it to transport Zelena right back to Oz.
Emma leaves a note for her family in the diner. Hook watches her from the shadows when Nimue reminds him that he knows what he has to do When Emma goes home, Hook is waiting for her. She tries to talk him out of his plan, but he just wants to thank her. If she hadn’t made her the Dark One, he would have never become the man he wanted to be. Emma swears to protect her family and attempts to stab him with the sword. Hook disappears and reappears as Henry and Emma can’t stab him. Snow finds the note, but before they can do anything, the Dark Ones come to lead them to the lake.
Emma shows up and Nimue tries to stop her from interfering with plan. Hook watches as Emma suffers, but he changes his mind. He takes all of the darkness into Excalibur and sacrifices himself. He tells her to drive the sword through him, killing him.
The sword destroys itself everything goes back to normal for the most part. Emma is a mess and at home she can hear the dagger calling . She goes to Rumple and he pulls out the dagger, which has his name on it. Rumple turned Excalibur into a conduit, so while Hook thought it was destroying darkness, he was really just moving it to Rumple. Now Rumple has the power of every Dark One who has ever lived. Emma forces him to open the portal to the underworld, threatening his relationship with Belle. And the whole family goes into the Underworld to get Hook.