VIDEO: Sneak Peek - 'The Doctor' Episode of ABC's ONCE UPON A TIME

On Sunday's episode of ONCE UPON A TIME titled "The Doctor," while Regina continues to try and stop using her magic in an attempt to win back Henry's affections, she begins seeing what she believes is a ghost from her past; and when Mary Margaret and Emma discover a lone survivor from an ogre massacre, Emma begins to question whether or not he's telling the truth. Meanwhile, in the fairytale land that was, Regina finds herself failing at learning the dark arts from a dark master because something from her past is preventing her from using her magic for evil. The episode airs SUNDAY, OCTOBER 28 (8:00-9:00 p.m., ET) on the ABC Television Network. Get a sneak peek below!

"Once Upon a Time" stars Ginnifer Goodwin as Snow White/Mary Margaret, Jennifer Morrison as Emma Swan, Lana Parrilla as Evil Queen/Regina, Josh Dallas as Prince Charming/David, Emilie de Ravin as Belle, Jared S. Gilmore as Henry Mills, Meghan Ory as Red Riding Hood/Ruby, and Robert Carlyle as Rumplestiltskin/Mr. Gold.

Guest starring are Raphael Sbarge as Archie Hopper/Jiminy Cricket, David Anders as Dr. Whale, Colin O'Donoghue as Killian Jones/Hook, Sarah Bolger as Aurora, JAMIE CHUNG as Mulan, Noah Bean as man, Sebastian Stan as Jefferson, Yurij Kis as assistant and Paula Giroday as Trish.

"The Doctor" was written by Edward Kitsis & ADAM HOROWITZ and directed by Paul Edwards.