Viewers were introduced to everyone's favorite fiery-haired mermaid on the latest episode of "Once Upon a Time."
On the latest installment, Snow (Ginnifer Goodwin) jumps into the ocean in order to escape the Evil Queen's (Lana Parrilla) henchmen. Snow is rescued by Ariel (JoAnna Garcia Swisher). Snow then thanks Ariel by encouraging her to reunite with her crush, Prince Eric, at the Under the Sea dance. But first, as the story goes, she makes a deal with the sea witch Ursula to get a set of legs to replace her fin.
When standing on two feet at the dance, she speaks to Eric (Gil McKinney), who is instantly taken by Ariel and invites her to join him on a voyage the next day. Ariel knows that her feet will turn back into a fin in a few hours, so she asks the sea witch for another day with legs. Regina then poses as the witch, and tricks Ariel into transforming Snow White into a mermaid.
When Regina comes back to gloat, Ariel stabs her with a dinglehopper. Later, Snow urges Ariel to meet up with Eric and tell him the truth about what she really is. But when Ariel goes to call for him, her voice is gone.
Back in Neverland, Hook (Colin O' Donoghue) tells the group that Neal (Michael Raymond-James) is on the island. Regina and Rumplestiltskin (Robert Carlyle) scheme to bring down Pan (Robbie Kay), but to do that, they need something from Rumple's shop in Storybrooke. Regina then summons Ariel for the task because mermaids can swim across realms. Regina restores Ariel's voice and promises to send her to Storybrooke, where she can get what's needed and reunite with Eric.
Meanwhile, Emma (Jennifer Morrison), Hook and the rest track Neal to Echo Cave, but they reach an impasse that can only be crossed if everyone shares their darkest secret. Hook reveals that he can now move on from his lost first love, Snow says she wants a baby, and Charming (Josh Dallas) reveals that he can't leave Neverland because he took the Dreamshade cure. Emma reveals that she doesn't want to deal with the heartbreak that she has gone through with Neal. Neal then shares his own secret: "I will never stop fighting for you, Emma."
On the next episode, "Dark Hollow," the story shifts back to Storybrooke. Ariel arrives in the town, where Grumpy discovers her. Belle (Emilie de Ravin) will help Ariel in her quest to save Henry, as well as find her true love, Prince Eric. But just as Belle and Ariel start to become friends, two men--played by James Immekus and Matt Kane--point guns at their heads and tie them up.
Freya Tingely, who guest-starred last season as Wendy Darling, will also appear in the episode.
In Neverland, the promo shows Neal screaming Emma's name as she ducks under a shadow during their journey to Dark Hollow.
Josh Dallas also told TVGuide that there will be another look into Snow and Charming's past-- specifically the day of their wedding, when Regina threatens them with the curse. "We're going to open up right after they get married," Josh Dallas teased. "Snow wants to get back at Regina for destroying her wedding basically. Charming just wants to go on the honeymoon. He just thinks it's a threat coming from Regina, that's all it is at the moment."
A series of photos from the upcoming episode has been released, which you can see here.
Watch the promo for "Dark Hollow" below, which airs Sunday at 8 p.m. ET on ABC.