Things are about to get a lot more complicated in the Underworld! Last week “Once Upon a Time” reintroduced Ruby into the mix, and it sounds like the arrival of the fairytale character might somehow be connected to Zelena and Hades. Episode 18 of the hit ABC series will reveal that Ruby was in Oz with Mulan before ending up in the Underworld.

According to the synopsis for Sunday’s installment, titled “Ruby Slippers,” a flashback will expose what Ruby (Meghan Ory) and Mulan (Jamie Chung) have been up to in the fairytale world. The two warriors somehow end up in Oz where they meet Dorothy (Teri Reeves) and discover that Zelena (Rebecca Mader) has returned. The trio join forces to figure out a way to defeat the wicked witch, but Dorothy “mysteriously disappears.” It’s when Ruby goes out to look for her that she ends up in the Underworld.

Is Ruby dead? Did she fall through a portal? Was Emma (Jennifer Morrison) the one that created the portal when trying to use her magic? The answer is unclear, but Ruby will quickly team up with her old friends to search for Dorothy.

That won’t be the only drama going on in episode 18. Snow (Ginnifer Goodwin) and David (Josh Dallas) are still conflicted over being apart from their son. After losing Emma at that age, the two are determined to be there for Neal. The only problem is that Mary Margaret’s name is etched on a gravestone in the Underworld, and Hades (Greg Germann) is preventing them from leaving. However, the two hatch a plan that could potentially allow one of them to “escape the Underworld.”

“Once Upon a Time” Season 5, episode 18 will air on ABC Sunday, April 17. Watch the promo video and sneak-peeks below: