As Hades becomes more powerful, it is assumed that Storybrooke is going to be in deep trouble in "Once Upon a Time" season 5 episode 21.

"Once Upon a Time" season 5 episode 21 is entitled "Last Rites." According to Spoilers Guide, Henry, Robin, Regina, David, and Emma return to Storybrooke and joins Snow once again. However, they are set to have a problem, as they still need to come face to face with Hades.

As per the publication, the Greek god of the underworld pursues deceiving Zelena as he sets up his plot of unleashing the power of the Olympian Crystal to conquer the town. While the heroes aim to find a way to take down Hades, Hook is busy searching for the missing pages of the storybook in the Underworld to help defeat the villain.

In addition to the heroes' efforts on defeating Hades, it is also revealed that Robin and Regina are set to do things in a more direct manner and this shall lead to an epic conquest that will change the heroes' lives for good.

Previously, Emma and Hook's love was tested in gold in "Once Upon a Time" season 5 episode 20. Entitled "Firebird," the episode saw Hades asked the heroes to help him get Zelena back from Peter Pan and Rumplestiltskin, with taking their names off the tombstones in return, as per Spoilers Guide.

In the episode, Hook was unable to leave the Underworld, so he and Emma walked its depth. It was also revealed that Cruella De Vil was eager to keep the trapped heroes in the Underworld.

"Once Upon a Time" season 5 episode 20, "Firebird," aired on May 1 while episode 21, "Last Rites," airs on May 8.