The Storybrooke heroes are out of the Underworld, but that doesn’t mean they’re safe. Hades managed to come to town with Zelena, and the gang has to stop him before he sets a new evil plan in motion in Season 5, episode 21 of ABC’s “Once Upon a Time.”

When viewers left off last Sunday, Hades (Greg Germann) tricked Emma (Jennifer Morrison) and Hook (Colin O’Donoghue) into going below the Underworld to find a cure to allow the pirate to return to the land of the living. But it turned out that the heroes weren’t the only ones Hades betrayed. The synopsis for episode 21, titled “Last Rites,” teases that he also lied to Zelena (Rebecca Mader).

While Zelena thinks that she managed to change the ruler of the Underworld, in reality he’s plotting to take over Storybrooke with the “all-powerful Olympian Crystal.” What exactly is the Olympian Crystal capable of? That remains unclear for now, and the heroes have no plans on finding out.

Everyone will quickly jump into action after arriving back in town through the portal. And they’ll also have help from down below. Although Hook was left behind in episode 20, he’ll still be searching for a way to defeat Hades while in the Underworld. He’ll need to look for the missing storybook pages that his brother tore out before finding the light.

Elsewhere, Regina (Lana Parrilla) and Robin (Sean Maguire) will take a “more direct approach” to get rid of Hades. The synopsis doesn’t reveal specifics about what they have up their sleeves, but the promo video teases that someone won't make it out alive after the “epic showdown.” 

“Once Upon a Time” Season 5, episode 21 will air on ABC Sunday, May 8 at 8 p.m. EDT.