'Once Upon a Time' season 6 episode 4 spoilers: Gold has secret connection to Mr. Hyde? Jasmine enters her new life

The upcoming episode of "Once Upon a Time" season 6 will delve into the untold story of Dr. Jekyll and Mr. Hyde. Will the episode reveal the dark secrets that lurk behind their odd transformation? Moreover, fans will see how Jasmine adjusts to her new life in Storybrooke.

Episode 4 titled "Strange Case" will give fans and viewers of the series a glimpse of that fateful day when Dr. Jekyll (Hank Harris) unleashed his inner beast, Mr. Hyde (Sam Witwer). In the promo trailer which appears below, the Evil Queen (Lana Parrilla) and Mr. Gold/Rumplestiltskin (Robert Carlyle) are shown to have witnessed when the doctor's experiment went haywire.

However, the trailer also has Mr. Hyde telling Rumple that he is not the monster. What did he mean by it? Was he implying that Rumple knows something and is hiding a terrible secret?

It can be recalled that in season 5, Mr. Hyde and Rumple made a pact in order to save Belle (Emilie de Ravin). Belle was under the sleeping curse, and apparently, Mr. Hyde knew a way to lift the spell, albeit an expensive one. It looks like in exchange for Belle's freedom from the curse, Storybrooke, Rumple, and perhaps the other residents of the idyllic town will be obliged to the doctor's evil alter ego.

The show's executive producer, Edward Kitsis, previously revealed that Mr. Hyde will play a crucial part in the current season even though the show is going back to old school storytelling.

"This season is going to be different from past because it's not going to be Hyde comes to town, we fight with him for 10 episodes, and then in the winter finale, he dies and we move on. We are changing around what we're doing this year and going back to that season 1 mentality of small town stories and smaller arcs," he told Entertainment Weekly.

Meanwhile, the same episode will feature Snow (Ginnifer Goodwin) working alongside Jasmine (Karen David) at Storybrooke Elementary School. It looks like Jasmine will be working as a school teacher, with Snow playing her mentor. TV Line released photo stills from the episode, which showed the two princesses bonding inside the school's cafeteria.

In related news, Hook (Colin O'Donoghue) will try to protect Belle from Mr. Gold after she finds herself trapped inside a pirate ship. As per Spoiler TV, it looks like Mr. Gold did something to keep her trapped in the ship. Belle has previously announced she doesn't want anything to do with Mr. Gold anymore even if she still loves him because they can never be good for each other.

Elsewhere, Emma (Jennifer Morrison) will be gearing up for her new life with Hook after the latter accepted her invitation to move in together.

"Once Upon a Time" season 6 airs Sunday, Oct. 16, at 8 p.m. EST on ABC.