"Where Bluebirds Fly" is the eighteenth episode of the sixth season of ABC's Once Upon a Time and the one-hundredth and twenty-ninth episode of the series overall. It aired on April 23, 2017. It was written by David H. Goodman & Bridgette Hales and directed by Michael Shultz.
In flashback, Zelena befriends a young woodcutter who has been cursed and turns to her for help finding a new heart. Zelena is forced to choose between keeping her powers and her friendship with him. Meanwhile, in Storybrooke, Zelena decides to take on the Black Fairy and put a stop to her, once and for all, against Regina’s wishes, and the Charmings disagree over Emma and Hook’s wedding plans.
The Storybrooke events take place after "Awake" while the events in the Land of Oz occurs during the flashbacks that took place between "Sisters" and "It's Not Easy Being Green" and later on in the recent timeline between "Heart of Gold" and "Our Decay".
In The Characters' Past
In Oz, a young Zelena is testing out her magic on a bird's nest by restoring it back on top of a tree after a group of kids knocked it off. When a young boy named Stanum sees Zelena, he tells her that he likes her, regardless of whatever the children say about Zelena, who they see as a freak. Flash forward years later, where a now adult Zelena (now the Wicked Witch at this point) received a surprise visit from a adult Stanum, this time requesting her help. He explained to Zelena that the Wicked Witch of the North cursed him and is slowly turning into a tin man. Stanum is seeking out the Crimson Heart, which could restore him to human form, but moments after Zelena turned him down, Stanum accused her of being afraid, prompting Zelena to change her mind.
During their quest, Stanum tells Zelena that she doesn't have to be lonely but she is doing her best to deny his advice. Suddenly, a lion comes of nowhere to attack Stanum, and Zelena uses her magic to make the lion go away (at this point the lion has become as Zelena would put it, cowardly). When they finally arrived to the location of the Crimson Heart, the two learned that the only way to make it work is through the absorption of another person's magic. Unfortunately Zelena's actions and selfish greed for magic causes her to betray Stanum, whom she suspect was aligned with Dorothy (at this point has not returned to Oz yet) by keeping the Heart for herself, leaving Stanum to transform into the Tin Man permanently.
At Zelena's farmhouse, Zelena is ready to give Robin her bottled milk, when she is surprised by the Black Fairy, who is holding her child. She offers Zelena a chance to join her in the final battle against Emma, but Zelena is furious with her unwanted visitor and asks her to leave after she turned down the offer, knowing that this was far from over as the Black Fairy was concerned. At the same time, Emma and Hook's planned morning is interrupted; Snow is ready and excited to help plan Emma and Hook's upcoming wedding, which is followed by Regina asking them if they seen Zelena. Hook then gives the wand piece he bought back from Neverland to Regina for her to examine. However, Emma stops everyone right there and wants them to focus on the wedding and get their minds off the Battle for now.
At the Pawn Shop, Gold tells Belle about how Mother Superior, when she was the Blue Fairy, knew about how his mother turned to Darkness, but since he had to put Mother Superior into a coma in order to protect Gideon, Gold decided to research more on what his mother is planning. When Zelena stops by the shop, she asks Belle to watch Robin while she goes after the Black Fairy. Moments later, after she studied the fragments, Regina shows up at the shop and realizes that Zelena has gone, leading her to the mines, since she finds her sister there and is hunting down the Black Fairy. This leads to a fight between the sisters with Zelena escaping the scuffle just in time to find the Black Fairy and Gideon, who then holds back Regina while the Black Fairy shows Zelena how powerless she can be, admitting that she was using her in order for Zelena to make the wrong decision. The Black Fairy absorbs Zelena's unstable dark magic to create the crystals needed for the final battle, then she sends them back to the outside of the mines. This causes more tensions as Regina tells Zelena that she should go back to Oz.
Around the same time, David noticed the loft opened and find Henry still trying to write the final chapter but discovered he can't do anything to change the outcome, so David tells Henry its useless to do it but they're still bothered by the symbols that Henry drew in the book. Snow is looking at a series of venues to hold the wedding, but David isn't happy with his wife's ideas. Snow pulls him aside to voice her anger over this, but David says that the timing isn't right as long as the Black Fairy is in Storybrooke. Emma on the other hand, hears this and tells her parents that she's willing to wait until after the Final Battle.
Back at the Pawn Shop, Zelena is ready to take Robin and preparing to return to Oz, when she suddenly changes her mind after she created a tornado to take her back. She soon meets up with Regina, Emma, Snow, David, Hook, and Henry, and reveals that she still has the Crimson Heart (that was bought from Oz via the tornado), which she used to absorb all of her magic in order to render the crystals useless. Zelena decided to sacrifice her magic in order to help Emma and Regina by restoring the crystals in the mines, and it gets the attention of the Black Fairy and Gideon, while Emma noticed the fairy blade restored. After Zelena told them about what Gold did to Mother Superior, the three then visit the Pawn Shop, where after they convinced Gold and Belle, allowed Emma to use the wand blade's magic to free Mother Superior from her coma. At the same time, the Black Fairy sees this on her crystal ball and finally tells Gideon the truth about her real reason behind why she was banished by the Blue Fairy, and it is tied to how the Black Fairy abandoned Rumplestiltskin in the first place when he was an infant.