Pack your bags, “Once Upon a Time” fans. The hit ABC fairytale drama returns Sunday with the second half of its fifth season, and viewers are going on a wild journey to the Underworld.

“Once Upon a Time” has been on hiatus since early December. But after a couple month break, fans won’t want to miss any of the action. Emma (Jennifer Morrison), Snow (Ginnifer Goodwin), Charming (Josh Dallas), Regina (Lana Parrilla) and some of your other favorite heroes will be boarding a vessel headed straight for Hell. And this isn’t part of a relaxing, yet fiery, vacation. The group will be on a mission to rescue Hook (Colin O’Donoghue).

Episode 12, titled “Souls of the Departed,” airs Sunday. The synopsis says the midseason premiere will find the gang discovering their search for Hook will “be more difficult than they had anticipated.” Why would that be the case? The inhabitants of the Underworld, of course! Familiar faces, like Regina’s estranged mother, Cora (Barbara Hershey), will be returning to “hound our heroes at every turn.” The episode description teases that some of the souls trapped in the Underworld have unfinished business, while others have “quite personal vendettas.”

The new installment also will include a flashback to the Enchanted Forest when Regina was still running as the Evil Queen. The synopsis adds that someone from her past will resurface to present her with “the perfect birthday gift.”

Once Upon a Time The Evil Queen (Lana Parrilla) will be revisited in a flashback during the “Once Upon a Time” Season 5 midseason premiere. Photo: ABC

“Once Upon a Time” viewers will remember that the winter finale concluded with the Dark Ones marking the residents of Storybrooke. Those marked would get dragged to the Underworld when the moon reached its peak that night. However, Emma was determined to stop the Dark Ones before they claimed any living souls on land — and she had a deadly plan in mind.

With Regina’s help, Emma plotted to take all the darkness and have the former evil queen use Excalibur on her. But unfortunately for the two heroes, Hook and Nimue (Caroline Ford) figured out what they were up to. Hook managed to get his hands on Excalibur, leaving Emma back at square one. Regina had one last trick up her sleeve, though. She reminded Hook about his father and the man he always wanted to be. That prompted Hook to gather all of the magic of the Dark Ones in Excalibur and hand the sword over to Emma.

“Let me die a hero,” he told her. “That’s the man I want you to remember.”

Emma and Hook were able to exchange one last kiss and “I love you” before she plunged the sword into his chest. Hook’s sacrifice freed Emma of the darkness and stopped the marked Storybrooke residents from being dragged to the Underworld. But it also killed the pirate.

Hook’s death wasn’t the biggest shocker of the episode though. It was revealed that Gold (Robert Carlyle) had tricked everyone. He had Excalibur in his possession along with the power of every single Dark One. Emma discovered Gold’s betrayal and made a deal with him to keep the secret from Belle (Emilie de Ravin) — Gold would help her get to the Underworld to bring Hook back. As for the pesky rule that you must trade a life for a life? Emma revealed she plans to share a heart with Hook.

“Once Upon a Time” Season 5, episode 12 airs on ABC on Sunday, March 6 at 8 p.m. EST. Check out more photos from the midseason premiere below:

Once Upon a Time A flashback to the Enchanted Forest in Season 5, episode 12 of “Once Upon a Time.” Photo: ABC Once Upon a Time Cora (Barbara Hershey) will return when “Once Upon a Time” Season 5, episode 12 visits the Underworld. Photo: ABC

Once Upon a Time Regina (Lana Parrilla), Henry (Jared Gilmore) and Robin (Sean Maguire) in the Underworld during “Once Upon a Time” Season 5, episode 12. Photo: ABC