ZELENA THREATENS TO KILL HENRY IF HOOK - WHOSE LIPS HAVE BEEN CURSED - DOESN'T KISS EMMA AND DRAIN AWAY HER MAGICAL POWERS, AND IN THE FAIRY TALE LAND OF THE PAST, SNOW AND CHARMING GO IN SEARCH OF GOOD WITCH GLINDA TO HELP THEM DEFEAT ZELENA, ON ABC'S "ONCE UPON A TIME"

"A Curious Thing" - Zelena threatens to kill Henry if Hook - whose lips have been cursed by the Wicked Witch -- doesn't proceed with kissing Emma, which will drain all of her magical powers away, and things begin to heat up between Regina and Robin Hood. Meanwhile, back in the Fairy Tale Land that was during the past year, Snow and Charming go in search of Glinda, the Good Witch of the South, to see if she can help them defeat Zelena, and the curse that will ultimately send the Fairy Tale characters back to Storybrooke is cast -- but from an unlikely source, on "Once Upon a Time," SUNDAY, APRIL 27 (8:00-9:00 p.m., ET) on the ABC Television Network.

"Once Upon a Time" stars Ginnifer Goodwin as Snow White/Mary Margaret, Jennifer Morrison as Emma Swan, Lana Parrilla as the Evil Queen/Regina, Josh Dallas as Prince Charming/David, Emilie de Ravin as Belle, Colin O'Donoghue as Hook, Michael Raymond-James as Baelfire/Neal Cassidy, Jared S. Gilmore as Henry Mills and Robert Carlyle as Rumplestiltskin/Mr. Gold.

Guest starring are Lee Arenberg as Leroy/Grumpy, Beverley Elliott as Granny, Sarah Bolger as Aurora, Rebecca Mader as Zelena, Sunny Mabrey as Glinda, Julian Morris as Prince Phillip, Sean Maguire as Robin Hood and Christopher Gauthier as Smee.

"A Curious Thing" was written by Edward Kitsis & Adam Horowitz and directed by Ralph Hemecker.

"Once Upon a Time" is broadcast in 720 Progressive (720P), ABC's selected HDTV format with a 5.1 channel surround sound. A TV parental guideline will be assigned closer to the airdate.

For more information on "Once Upon a Time," visit ABC.com/Once