Who is the Author on “Once Upon a Time”? Regina (Lana Parrilla) is dying to know … and so are fans! The identity of the man or woman remains a mystery for now, but it’ll be a major plotline moving during the remaining episodes of Season 4.

Viewers were introduced to the magical fairytale book during Season 1 of the ABC series. The book has resurfaced in every season, but became a serious player in the story line during Season 4 when Regina revealed her plans to change her ending with Robin Hood (Sean Maguire). The book set the rule that villains don’t get happy endings – but what about if a villain joins the good side?

Henry (Jared S. Gilmore) joined Regina’s cause, labeling it “Operation Mongoose.” He got a job at Mr. Gold’s (Robert Carlyle) shop in order to search for some clues, but ultimately found nothing. However their bad luck turned around during the winter finale when Henry, Regina and Emma (Jennifer Morrison) stumbled across a secret library in the Sorcerer’s mansion. The room held volumes of empty books, all ready to be filled in by the Author.

Unfortunately Operation Mongoose still has a lot of roadblocks in the way.

“This is a quest that has been quite difficult for Regina,” Lana Parrilla revealed to Entertainment Weekly. “With all the research she’s done thus far and Operation Mongoose, she keeps hitting dead end after dead end. She’s lost some faith in ever finding the author, but she’s still not going to give up.”

Parrilla added that Henry is the thing keeping her character going. Because he believes in the mission so much, he’ll play a factor in getting to the bottom of the mystery.

“They work together and start finding clues leading to the discovery of this author, so that will play out for the remainder of the season,” Parilla continued.

But as “Once Upon a Time” fans know, Regina and Henry aren’t the only ones searching for the Author. The winter finale concluded with Mr. Gold exiled from Storybrooke thanks to the pesky town border and his scorned wife, Belle (Emilie de Ravin). Gold traveled to New York City and sought out Ursula (Merrin Dungey). He revealed that he wanted to gather the Queens of Darkness – Ursula, Cruella de Vil (Victoria Smurfit) and Maleficent (Kristin Bauer van Straten) – to find the Author and force him to rewrite the rules for villains. The rewrite would allow them to re-enter Storybrooke and wreak havoc on the poor townsfolk.

“Once Upon a Time” Season 4 returns to ABC on Sunday, March 1 at 8 p.m. EST. Are you excited about the Author plotline? Tweet your thoughts to @AmandaTVScoop.