Once Upon a Time is freezing over — literally.

In a desperate attempt to locate her missing sister, Anna (Elizabeth Lail), Elsa (Georgina Haig) accidentally traps Emma (Jennifer Morrison) in an ice cave and things go south as the dipping temperatures put her in grave danger. With Regina (Lana Parrilla) abandoning her duties as mayor and focusing on her troubles with Robin Hood and Marian, the townspeople turn to another to lead Storybrooke: Mary Margaret (Ginnifer Goodwin).

Read more 'Once Upon a Time': 10 'Frozen' Moments From the Season 4 Premiere

The Hollywood Reporter exclusively debuts a scene from Sunday's episode, "White Out," wherein Mary Margaret faces her first big test: trying to restore power to the town after Elsa freezes the power lines. Her struggles to solve the problem are noted by Happy (Mike Coleman), Grumpy (Lee Arenberg) and Granny (Beverley Elliott), who suggest other Plan Bs (Gepetto, Dr. Will), angering Mary Margaret in the mean time.

Read more 'Once Upon a Time' Stars and Creators Tease 'Frozen' Arc's "Emotional Roller Coaster"

When Happy rattles off all the things they won't be able to use due to the power outage, such as "TV, DVD, CD, DVR, DVD," Mary Margaret — running on minimal sleep and acclimating to being a new mother — has a full-blown freakout. "Stop saying letters!"

Note to self: Don't piss off Snow.

Once Upon a Time airs 8 p.m. Sundays on ABC.

Email: Philiana.Ng@THR.com

Twitter: @insidethetube