A royal ball is held in Camelot, but a dark turn of events forces David and Robin to take action. Meanwhile, Regina's fortitude is tested as she tries to safeguard Emma; and back in Storybrooke, Hook attempts to bring Emma back to the light.
Emma and Regina devise a plan to free Merlin, but they lack a pivotal ingredient. Meanwhile, Mary Margaret and David seek an important dagger; Henry asks Violet to go on a date; and Merida attempts to carry out a covert mission Emma has assigned her.
A surprise visit from hooks brother Liam May provide Hook and Emma with the tools they need to defeat Hades; and in flashbacks, the bond between the Jones Brothers is tested as their merchant ships head into a storm.
Belle turns to Rumplestiltskin with hope of finding a way to protect their child from Hades. However, they disagree over whether to use dark magic, as Belle forbids Rumplestiltskin from using his powers for evil.
In flashbacks, Ruby and Mulan find themselves in Oz, where they meet Dorothy. After the three witness Zelena's return to Oz, they look for a way to defeat her once and for all. However, Dorothy mysteriously disappears.
Now that Hades and Zelena have been reunited, Hades tells Zelena about his plan to leave the underworld forever and Cora reveals information from the past that will change the lives of Regina and Zelena forever.
Emma, David, Regina, Robin and Henry are finally back home in Storybrooke and reunited with Snow, but, unfortunately, they still have to contend with Hades, who continues to deceive Zelena as he lays out his plan to use the all-powerful Olympian Crystal to take over the town. The heroes desperately search for a way to defeat Hades while Hook does the same in the Underworld, looking for those missing storybook pages. Regina and Robin take a more direct approach, which culminates in an epic showdown that will leave our heroes forever changed.