“Happily ever after” has never been further out of reach. When Once Upon a Time—ABC’s fantasy series about fairy-tale characters—unveils its marketing campaign for Season 5 at Comic-Con, viewers’ worst fear will be confirmed: Emma Swan (Jennifer Morrison), aka the Savior, is poised to become the show’s scariest baddie yet. “As formidable as Emma was as a hero, she’s going to be exponentially more dangerous as a villain,” promises executive producer Adam Horowitz. Fellow executive producer Edward Kitsis adds with a laugh, “I hope our fanbase reacts well—it seems like a large segment is very worried!”

And with good reason. The September 27 premiere, titled “The Dark Swan,” will pick up moments after last May’s finale left off, as Emma allowed the evil spirits that were released from Rumplestiltskin (Robert Carlyle) to enter her body and transform her into the new Dark One. “The first thing Emma wants to do is get the darkness out,” Kitsis says. “But will she be able to resist taking a bite of the forbidden apple?”

Uh, that’d be a no, meaning that Emma’s nearest and dearest—including her son Henry (Jared Gilmore), true love Hook (Colin O’Donoghue) and enemy-turned-ally Regina (Lana Parrilla)— will be tasked with finding the mysterious sorcerer Merlin, the only one capable of breaking the curse. Hint: The gang should set their GPS for the Camelot of Arthurian legend—and be prepared to encounter some of its famed residents along the way. (Think King Arthur, Princess Guinevere, Sir Lancelot and the Knights of the Round Table.) “We’re excited to put our twist on these classic characters,” Kitsis says. “We love the origin stories!”