Colin O'Donoghue, Jennifer Morrison Colin O'Donoghue, Jennifer Morrison

Storybrooke's so-called savior needs a little work. 

On Sunday's Season 4 premiere of Once Upon a Time, town sheriff Emma (Jennifer Morrison) couldn't quite keep order when Frozen's ice queen Elsa (Georgina Haig) hit Storybrooke and unleashed one of her angst-driven snow monsters upon the unsuspecting populace. Unfortunately, Emma's attempts to tap into her own magical powers didn't even leave a dent in the chilly creature.

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Should fans be worried that Emma can't keep Elsa in check? "It's definitely going to be a moment of concern for her," Morrison tells TVGuide.com. "I think she only has struggled emotionally, internally about what she even wants to do about having these powers in the first place. When she's put on the spot like she was with the snow monster and she does her best in the moment, she doesn't really know how to harness what's inside of her."

Emma had better hurry up, though. Judging by a preview clip for next week's episode, Elsa's anxieties strike again — but instead of a snow monster, she creates a deep freeze that leaves Emma curled up and shivering in a fetal position. "Elsa's fear takes over and because of that fear, we end up in a life-threatening situation," Morrison explains. "Obviously Elsa isn't affected by the cold the same way a normal human being would be, but the cold does affect Emma, so she ends up trapped in a situation where everyone is scrambling to try to get Emma out of the potential freezing situation."

Initially, Once Upon a Time's producers had planned on filming that upcoming scene in a meat locker, in order to capture the characters' breath on screen. "But they realized that they [shouldn't] see Elsa's breath because she isn't affected by the cold, so that wouldn't make any sense," Morrison reveals. "They would still have to CGI out her breath and keep my breath. And also, that would've been horrible to actually be freezing all day. I was very, very grateful that they changed their minds about that." 

Instead, the scene was shot on one of the hottest days of summer — about 104 degrees outside — in Vancouver. "We were on stage, and the air conditioning couldn't keep up. And we had to turn the air conditioning off during the take anyway," says Morrison. "We were on the green-screen stage, and it was like 110 degrees in there. I was sweating through t-shirts every take because you shiver to keep warm, but I was already so hot. And then I was fake-shivering through every take for 16 hours. I was so sweaty and gross! [Laughs] I couldn't have been hotter while I was 'freezing to death.'"

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However, all is not lost, despite Emma almost becoming a human popsicle. As creators Adam Horowitz and Edward Kitsis teased before the season began, that inability to control her power will give her common ground with the very person who has put her in jeopardy. "Elsa has a power inside of her that she's not sure what to do with and took her a long time to learn how to control and how to understand it," Morrison says. "So Elsa's going to be a crucial friend to her in terms of how to start to focus that power and figure out what to do with it. But there's definitely going to be a bump in the road where Emma doubts herself a little bit about all of it."

Once Upon a Time will also provide more insight into what makes the complex Emma tick when it delves into her formative teenage years (played by actress Abby Ross) this season. "In the few episodes that we've shot, we've gotten some really big pieces of information that we'd not had in the past," she teases. "We are going back to her younger days and [we] find that she figures some things out."

Meanwhile, Emma has other problems to contend with in the present. After saving the life of the doomed Maid Marian (Christie Laing) in the past by bringing her to Storybrooke present, she unwittingly mucked up the burgeoning romance between Regina (Lana Parrilla) and Robin Hood (Sean Maguire), who had already mourned his wife's passing but now must honor his vows. Once again, Regina has been denied a happy ending, and Emma feels responsible. But can she keep her friend from reverting to her Evil Queen ways? 

"Emma can't apologize for saving a life, and I don't think she regrets saving a life," Morrison says. "But Regina has been through so much and she fought so hard, and then to have another love taken away from her the way she lost her first love, it's truly devastating. I think it's totally fair that she's as hurt and confused at this moment as she is. Emma really does appreciate her friendship with Regina and she does want to protect Regina's relationship with Henry and help her stay in a place where she can continue to be a wonderful mother to him."

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After all, Emma can't begrudge her friend's happiness when her own love life finally seems to be going well. Last season, Killian Jones, aka Captain Hook (Colin O'Donoghue), gave up his ship for her and was rewarded with a kiss. This season, Emma and Hook will take their flirtation to the next level when they start to date, which has been a long time coming after Emma's less-than-successful relationships (almost getting engaged to a flying monkey!) in the past.

"She's more comfortable than people would expect," Morrison observes. "She's also been through a lot with Hook at this point. They've been on great adventures and they've traveled through worlds, they've traveled through time. He's given up his ship for her, he's proven that he's someone who really continues to show up for her. Like Emma, he's made some mistakes in life, some terrible mistakes in life, and has worked very hard to redeem them. I think she relates to the fact that she's also made mistakes in her life and she's worked very hard to redeem them. So they do have that in common. She believes in that part of him the same way she believes in that part of herself. So there is definitely an openness to her when they do finally decide to go on this date."

As for their first date itself, Morrison categorizes it as "super romantic" and confirms that Hook will put aside his usual Hook leather outfit in exchange for more modern attire. "Yes, he decides to make quite the effort for our first date," she says. 

Are you excited to learn more about Emma's past? What do you think her magical powers will look like in full force? Any guesses as to what Emma and Hook's first date will look like? Share your thoughts in the comments below!

Once Upon a Time airs Sundays at 8/7c on ABC. 

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