The Season 4 fall finale of "Once Upon a Time" ended the show's heroes and villains starting a race to find the storybook author who decides who gets happy endings. 
Rumpelstiltskin (Robert Carlyle) and the Queens of Darkness stand 
plotting in one corner, determined to rewrite history for the villains. 
Meanwhile, reformed bad girl Regina (Lana Parrilla) has found support 
from Emma (Jennifer Morrison) and the rest of the Charming heroes to 
help her get her happy ending and reunite with her true love Robin Hood 
(Sean Maguire). 
While the contest seems like a classic good versus bad matchup, executive producers Eddie Kitsis and Adam Horowitz assure Zap2it
 that it won't be that easy. "Once Upon a Time" is reevaluating whether 
good always beats evil, and some of the show's previously established 
heroes might actually be more villainous than they appear.
"Is [being a hero or villain] based on a title or is it based on 
our actions? We are going to see in the second half villains doing 
surprising things and heroes doing surprising things," Kitsis says. 
Parrilla has already clued us in that Regina will struggle with her light and dark sides,
 but she is by far not the only one that falls into the ambiguous 
category when it comes to Storybrooke characters. Hook (Colin O' 
Donoghue) also slides along the good to evil spectrum, and there's also 
Ruby (Meghan Ory) and Will Scarlet (Michael Socha) who are caught in the
 middle righteousness and vice. But surprisingly it will be done of 
these gray characters who will have the most trouble when it comes to 
choosing sides. 
"I think it will be Snow White and Prince Charming," Kitsis admits. 
Say what? If there are any two people that exemplify the title of 
hero it is clearly the Charmings. Regina has a book of quips on how sick
 their eternal belief in hope and goodness makes her. Surely Snow 
(Ginnifer Goodwin) and Charming (Josh Dallas) couldn't be tempted by 
Rumple and his new partners in crime ... right?
"As far as you've seen!" Kitsis answers. "I don't think you've seen all of their flashbacks." 
The aforementioned flashbacks will take audiences back to Season 1 
in a time before the curse, both in Storybrooke and the Enchanted 
Forest. Kitsis and Horowitz have revealed that Snow White and Charming 
have a secret past with Maleficent (Kristin Bauer van Straten), Ursula 
(Merrin Dungey) and Cruella de Vil (Victoria Smurfit). They think this 
new trio are the necessary characters to bring some of the Charmings' 
dark secrets to light.Source
