Once Upon a time season 5
Once Upon a time season 5 will premiere on 27 September on ABCABC

Once Upon a Time season 5's premiere may see Emma Swan become the Dark one, but Henry and Hook will not rest until they bring her back from the dark side.

The season 4 finale ended with Emma saving Regina from darkness, and she used the dagger to consume her, thus making her the Dark One.

But before giving into the dark side, Emma told Hook that she loves him and that she would never lose hope in him, and that her parents and Hook will find a way to save her.

According to a new report, Merlin – aka Sorcerer – will reportedly play a main role in the upcoming season, as he is the only one who can save Emma Swan (Jennifer Morrison) from darkness.

A TVLine report states that Merlin's role will be played by a "Black Brit" in his 30s or 40s with a "natural British accent". The website claims that the character could be highly intelligent with "great wisdom".

Hook and Henry may find Merlin, who in turn will help them bring Emma back out from the dark side.

A new fan theory meanwhile, predicts the same, as season 5 will take viewers to Camelot in search of Merlin.

According to the theory, Hook, Snow White and David would find Merlin in Camelot, where the would explore more places and eventually find the Holy Grail.

The fan has also mentioned the base for this theory, which is "what the Apprentice told them about Merlin and the necessity for them to find him. This must be to where S5 is going".

In another suggestion, Hollywood Reporter states that season 5 will arguably have the worst "big bad" the show has ever seen.

"Though Regina and Rumple have been Big Bads, when that happened, many of their relationships with the people of Storybrooke were complicated, at best. For Emma, she has been the savior. She has her parents, her son, Hook, and friends. How will they deal with trying to save her? And what will Dark Emma be able to put them through?" said the website.

Although it will not be easy for Hook and Henry to save Emma right away, fans are sure that their love will bring her back.

Here are a few tweets that predict the plot for season 5.

Once Upon a Time season 5 premieres on 27 September 2015.