Colin O'Donoghue, Jennifer Morrison

Once Upon a Time's fairy tale characters might be in even more trouble!

When Emma (Jennifer Morrison) and Hook (Colin O'Donoghue) are sucked into Zelena's (Rebecca Mader) time portal during Sunday's two-hour season finale (8/7c on ABC), the dynamic duo will find themselves in the Enchanted Forest of the past, where they'll quickly discover that their arrival could endanger the future. Seeking Rumple's (Robert Carlyle) help, Emma must admit that they've already meddled in the wrong places. But whose past have they changed? Check out an exclusive sneak peek at the season finale below:

Lightning Round 13: Once Upon a Time bosses answer your burning questions

Once Upon a Time's two-hour season finale airs Sunday at 8/7c on ABC.