Feeling their pain from having lived through the same experience, Emma desperately tries to help two homeless children find their birth father before they’re separated and put into the foster care system. Meanwhile, back in the fairytale world that was, the Evil Queen coerces Hansel and Gretel into stealing an important artifact from a blind witch.

Emma, Regina, Mary Margaret, David, Robin, Henry and Gold arrive in the Underworld, on a mission to rescue Hook, only to discover that their search will be more difficult than they had anticipated. The inhabitants of the Underworld — all souls with unfinished business and many with quite personal vendettas — hound our heroes at every turn. Meanwhile, in an Enchanted Forest flashback, a familiar face from the Evil Queen’s past returns to present Regina with the perfect birthday gift.

The heroes join forces with an old friend of Snow's to defeat an obstacle standing in the way of finding Hook. Meanwhile, Hook encounters challenges of his own.

Emma, Snow, David, Regina, Robin, Henry and Hook continue to search for a way to free everyone from the Underworld. At the mercy of Hades, Gold creates a portal to Storybrooke, which transports Belle, Zelena and Baby Hood to the Underworld. While Zelena and Regina get into a sibling squabble, Belle is reunited with Rumple only to learn some tremendously shocking news that will change her life forever. Meanwhile, Snow and David hopelessly attempt to send a message from the Underworld to their son, Neal. In flashbacks, Hades learns about Zelena’s very special spell and pays her a visit in Oz with the intention of striking an alliance, but finds himself with more than just a partner in crime.

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, and Ruby’s search for her new friend lands her in the Underworld. Reunited with the heroes, Ruby teams up with Emma, Regina and Snow to continue looking for Dorothy. Meanwhile, Snow and David struggle with not being able to be with their son, Neal, and devise a plan so that one of them can escape the Underworld.

Hades turns to the heroes to ask for help with getting Zelena back from Rumplestiltskin and Peter Pan. In return, he offers to take all their names off their tombstones. However, when Hook is still unable to leave, he and Emma must journey into the depths of the Underworld. Meanwhile, Cruella De Vil is determined to keep the heroes trapped in the Underworld. In flashbacks, Emma searches for answers about her family and makes an unexpected friendship.

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.