Hades made quite the proposal in episode 19 of “Once Upon a Time.” The Season 5 installment of the hit ABC series has been full of twists in the Underworld, but fans certainly didn’t see this coming.

Sunday night’s episode, titled “Sisters,” kicked off with Hades (Greg Germann) whisking Zelena (Rebecca Mader) away for a romantic picnic on the outskirts of town. Zelena initially thinks that Hades is simply trying to get physical with her, but the lord of the Underworld wants more from the wicked witch. Getting down on one knee, Hades makes the proposal of a lifetime.

“Will you make chaos with me?”

It’s an offer that comes with a lot to think about. Hades reveals that he wants to leave the Underworld and live in Storybrooke with Zelena once his heart begins beating again. But he knows that the heroes would never let him walk among them. That’s why he put all of their names on tombstones. After Snow White (Ginnifer Goodwin) and David (Josh Dallas) swapped their names the week before, he wanted to make sure no one else could escape.

Is a future with Hades what Zelena really wants? She doesn’t answer yes or no. And unfortunately for her, Hades’ proposal is made public thanks to Regina’s (Lana Parrilla) magic mirror.

Although the sisters are not on the best of terms, Regina begs Zelena to stay away from Hades and not take him up on his offer. But Zelena thinks that Hades can be saved. Regina doesn’t have the same optimism and tells her sister there is no way she can redeem the god of death.

Since Zelena has no plans on listening, Regina’s forced to turn to the others to hatch a plan to keep Zelena and Hades apart. And surprisingly, that plan involves Regina and Zelena’s mother, Cora (Barbara Hershey).

With Hook’s (Colin O’Donoghue) help, Regina is able to free Cora from the mill that Hades is forcing her to work in. Once out of her rags, Cora reveals that the only way to separate Zelena and Hades is to make Zelena forget about her love for him. She takes Regina to a river in the Underworld that has the ability to make the person who drinks from it forget. She explains that all they need to do is get Zelena to drink it. But that’s not the only time that Cora slipped someone water from the river.

A flashback reveals that a young Regina found Cora’s wand and made a wish for a sister. The spell accidentally cursed her, and the only person who could lift her out of the curse was a relative with magic — Zelena.

Cora went to Oz where she found a teenage Zelena being verbally abused by her adopted father who didn’t like her using magic. She froze the man and asked Zelena to prove she can use her magic for good by helping her daughter. Unaware of who Cora really was, Zelena agreed to accompany her to the Enchanted Forest to help. Zelena’s magic worked and the curse was lifted from Regina. The two girls even bonded in their short time together, however, when they figured out that they might be related, Cora put a stop to things. Lecturing Regina for not depending on herself, Cora makes guards remove Zelena before slipping both girls water from the river.

Back in the Underworld, Regina is confused about how to slip Zelena the water. Cora suggests it’s time she pays a visit to her estranged daughter. Of course, Zelena is not happy to see the woman who abandoned her, but Cora forces her way inside. Once alone with her daughter, Cora apologizes for giving her up and tries to make amends. Meanwhile, Regina is hiding and waiting for her chance to slip Zelena the magical water. Unfortunately, their plan doesn’t work. Knowing that Regina is hiding in the other room, Zelena tosses the water into the flames. She accuses her mother of lying to her once again, but Cora argues otherwise. She uses her magic to show them the memory of when they were sisters who loved each other.

It’s a touching moment that brings Zelena and Regina together and allows Cora to step into the light. Regina even goes as far as to encourage her sister to go to Hades and try to change him into a good man. But Gold (Robert Carlyle) has other plans for the former Wicked Witch of Oz. Blaming her for Belle’s (Emilie de Ravin) sleeping spell, Gold enlists the help of Peter Pan (Robbie Kay) to kidnap her.