"Once Upon a Time" season 5 is set to return to the small screen with its 100^th episode, and the trailer for the upcoming episode titled "Labor of Love" which was released recently could not have been any more thrilling.

"Labor of Love" is bringing back some of the characters in the series, as the characters of Storybrooke make their way into the Underworld to make a pitch for Emma who is there to deliver Hook.

Based on the trailer, Hercules will also make a special appearance in the episode. This comes after Snow and David walks around the Underbrooke's Cemetery and accidentally comes across the grave of the popular Greek figure. Believing that Hercules is the only character stalwart enough to throw a curve at the villains, they decide to breathe life into him again. But the catch is that the reincarnated Hercules seems not to be in his right mind, so Snow still has a lot of work to do.

Aside from Hercules' reincarnation, the trailer also shows Regina having her own share of adversities being in the Underworld. As she comes face to face with her past enemies, the strength of her character will be put to test.

Together with Emma and the crew, Regina goes toe to toe with Hades, the God of the Underworld, to ensure that Hook goes back with them to the land of the living.

Meanwhile, Lana Parilla who plays Regina recently said in an interview that their group cannot afford to stay in the Underworld for long.

"The Underworld is not Hell. It's purgatory. You're in this limbo state. Everyone is warning them to leave because Hades wants to keep all the souls that are down there. If you don't get out quickly you can end up trapped down there as well," she said.

"Once Upon a Time" airs every Sunday night on ABC.