The film begins with a crew of ice harvesters collecting ice out from a frozen lake in the Scandinavian mountains ("Frozen Heart"). Among them is an 8-year old boy named Kristoff Bjorgman, and his reindeer calf Sven, who try to emulate the harvesters but are always shut out. After collecting enough ice, the harvesters load it onto their sled and depart, headed for the town of Arendelle.

The scene changes to the castle in the Kingdom of Arendelle. That night, 5-year old Princess Anna is restless, so she tries to wake up her 8-year old sister Elsa to play. Elsa playfully brushes her sister off until Anna mischievously asks, "Do you want to build a snowman?", to which Elsa delightfully agrees.

Movie Disney Frozen

The sisters run down to the ballroom and create a winter field of snow using Elsa's snow magic, enjoying their time with plenty of merriment. They build a snowman, who Elsa names Olaf, claiming "I like warm hugs!" The girls play gleefully with Olaf until Anna makes a leap Elsa wasn't prepared for, and the blast of power meant to create a pile of snow hits Anna in the head, knocking her unconscious and turning a streak of her hair platinum blonde. Their parents, King Agnarr and Queen Iduna rush in, responding to Elsa's cries of anguish. They check on Anna and she is cold to the touch. Agnarr and his wife hastily load both girls onto their horses and ride at full speed into the mountains.

As the royal family gallops through the forests at full speed, they pass by Kristoff, who is still being dragged on his sled by Sven. He is intrigued by the trail of ice left behind by one of the horses. He follows it into an empty clearing that appears to only be populated by a large assortment of moss-covered boulders. From the edge of the clearing, Kristoff watches the girls' parents appear to ask the boulders for help. Suddenly, the boulders all begin to roll into a circle around the royal family, then unfold themselves, revealing themselves to be the trolls. In fact, the "boulder" that Kristoff is hiding behind is revealed to be another troll, Bulda, who takes Kristoff and Sven in after deciding they are cute (and in part because Sven licks her).

Pabbie, the leader of the trolls, shows up and asks the King if Elsa was born or cursed with her abilities. He observes that Anna is lucky she was hit in the head, as a hit to the heart would have been fatal. He advises the family that it might be best to not have Elsa use her powers around Anna, and alters Anna's memories so she has no knowledge of her sister's powers, remembering only the fun they've had. Pabbie warns Elsa that her powers will grow, and although they are beautiful, they'll be dangerous if she cannot learn to control them, as fear will be her greatest enemy.

Subsequently, the castle is closed off to visitors. Staffing is reduced to a minimum, and Elsa is ostracized from everyone, including Anna, in order to protect her from the world until she can learn to control her powers, leaving both sisters distraught and lonely. Despite Anna's best attempts ("Do You Want to Build a Snowman?"), she is unable to rouse Elsa from her room. Their despair only escalates when, while Elsa is 18, their parents depart on a diplomatic mission for two weeks. They are killed when the ship they are on capsizes in a storm and is swallowed by a huge monstrous wave. Anna goes again to Elsa's door, pleading for consolation from her only remaining family member. But Elsa, though she sits sadly on the other side of the door, refuses to communicate with Anna.

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