“Once Upon a Time” fans have a busy night ahead of them Sunday. The hit ABC fairy-tale series is treating viewers to a special 2-hour event for Episode 8 -- and it’s one you definitely won’t want to miss.

According to the synopsis for Episode 8, “Smash the Mirror,” fans will finally get to see what happened between Elsa (Georgina Haig) and Anna (Elizabeth Lail) in Arendelle of the past. The Snow Queen, aka beloved Aunt Ingrid (Elizabeth Mitchell), previously told Elsa that it was Anna who trapped her in the urn -- could she be right? Judging by the synopsis, it’s definitely a possibility. The episode description teases that the Snow Queen will try to pit the sisters against each other, and when it “proves more difficult than she anticipates,” she resorts to “drastic measures.”

Meanwhile, in present-day Storybrooke, Emma (Jennifer Morrison) will continue to struggle with her powers. After Episode 7, Emma is afraid she’ll hurt a loved one with her lack of control. This will lead the Savior to turn to Mr. Gold (Robert Carlyle) instead of her friends and family. In a surprising move, Gold tells Emma about a “way to get rid of her powers altogether.” While that might seem like the only option open to Emma, Hook (Colin O’Donoghue) tries to put a stop to it before it’s too late.

But that’s not the only drama that “Once Upon a Time” fans can look forward to in Episode 8. As Mary Margaret (Ginnifer Goodwin) and David (Josh Dallas) search for Emma, Regina (Lana Parrilla) will continue her quest to find the storybook author. However, her mission “takes an unexpected turn.” Could it possibly have to do with Robin Hood (Sean Maguire)? The synopsis adds that Robin Hood will be on a mission of his own in “Smash the Mirror” -- when he enlists the help of Will Scarlet (Michael Socha).

“Once Upon a Time” Season 4, Episode 8 will be shown on ABC Sunday at 8 p.m. EST. The 2-hour special will take over “Resurrection’s” time slot, but conclude at 10 p.m. to accommodate “Revenge.”

Once Upon a Time Anna (Elizabeth Lail) will find herself behind bars in "Once Upon a Time" Season 4, Episode 8. Photo: ABC

Once Upon a Time Elsa (Georgina Haig), right, holds the beloved necklace that Anna (Elizabeth Lail) gave her in a photo from "Once Upon a Time" Season 4, Episode 8. Photo: ABC

Once Upon a Time Anna (Elizbaeth Lail), left, and Elsa (Georgina Haig) in a photo from "Once Upon a Time" Season 4, Episode 8. Photo: ABC

Once Upon a Time Elsa (Georgina Haig) in a photo from "Once Upon a Time" Season 4, Episode 8." Photo: ABC

Once Upon a Time Elsa (Georgina Haig) in a photo from "Once Upon a Time" Season 4, Episode 8. Photo: ABC