In flashbacks to Oz, a young Zelena meets a boy named Stanum. She uses her magic to save baby birds. When bullies mock her, Stanum scares them off with his ax. Several years later, once Zelena's claimed the throne and embraced her green skin, Stanum comes to Emerald City for help. The Wicked Witch of the North has cast a spell on him that's slowly turning him to tin. He asks Zelena to help him create a heart.
In Storybrooke, the Black Fairy visits Zelena. She wants her help. Zelena turns to Regina, and the other heroes. She knows where Black Fairy is hiding, and she wants to kill her. Regina attempts to talk sense into her sister. They need to defeat the Black Fairy as a team. But Zelena insists she can do it herself since her magic is the strongest. She asks Belle to watch Robin, and heads to the mines to find the Black Fairy.
Regina follows. The two fight and end up trapped. They discover the Black Fairy is hoarding fairy crystals. But they're light magic. She picks a fight with Zelena while Gideon distracts Regina. The Black Fairy easily overpowers Zelena and forces Zelena to use her magic to turn the crystals dark. She knew all along Zelena would make the wrong choice. Regina tells her sister she needs to return to Oz because they can't keep fixing her mistakes.
During the flashback, Zelena tries to help the Tin Man, but learns it will she will have to sacrifice her magic. She refuses. He turns into a statue even as he begs her to be good. She'd rather have her magic than friends. In Storybrooke, Zelena prepares to take Robin to Oz, but has a last minute change of heart. She goes to Regina and the others and tells them she will put her magic in the crystal heart, and then it will undo what the Black Fairy did.
Regina and Emma help Zelena cast the spell. They promise to look after Robin if something happens. It works. The three head to Gold's shop where Rumple and Belle have been keeping the Blue Fairy. Belle convinces Rumple to let them try and wake her. Emma uses the fairy crystal, and it starts her out. The Black Fairy watches from afar with Gideon. She knows if Blue wakes up, she can tell them her darkest secret: why she gave up Rumple as a baby.