Im form Denmark, so my english isn't the best, but I'm trying to do my best... Enjoy...
Prologue:
Jack Frost was flying restless around. Nobody was able to see him, and it had been like that for many years now. In front of him a gigantic castle was getting on sight.
He flew by the windows, most of the rooms where empty, but suddenly he came to a window, where he could see two girls sleeping. Soon he realized that only one of them was a sleep, because the youngest ran to the other girl's bed.
"Elsa… Pssh..." She crawled on top of the older girl. "Wake up, wake up, wake up…"
"Anna go back to sleep." The older girl, Elsa, said.
"I just can't, the sky is awake, so I'm awake… So we have to play…"
"Go play by yourself." Elsa said, pushing Anna down from the bed. Anna sat there for a moment, the she crawled back on top of Elsa.
"Do you want to build a snowman?"
Then they ran out of the room, and Jack followed them. They ran into a throne room, and Anna began yelling: "Do the magic! Do the magic!" Now the two girls had Jacks full intention.
Then Elsa began moving her hands around each other, and threw something that looked like a snowball into the air, and it transformed the throne room into a winter paradise.
Jack was so amazed that he didn't got to save Anna before Elsa hit her, with her ice magic.
"Mom! Dad! " Elsa cried holding Anna in her arms. Ice began covering the floor and the walls.
Their parents came running into the room, and Jack couldn't do anything but watch when the rode for help.
Trolls came rolling from everywhere, and an old troll used his troll magic to remove the ice from Anna. Then he began talking about Elsa's powers getting stronger and that fear would be her worst enemy.
Jack flew after this and began exploring the world again, but he kept returning to Elsa. He saw her losing every single bit of control, and her fear taking over her life.
There was nothing he wanted to do more than helping her, but after many tries, he gave up. She wasn't able to see him.
He saw the girl live her life in hell, and her life didn't get better when her parents died in a shipwreck.
Then at her coronation years later everything went wrong for her, and she fled from the place the was meant to rule.
The fled to at mountain where she found herself again, but accidently started an endless winter.
He saw her once again hit her sister with her magic, and getting attacked by soldiers trying to kill her, ending up in a prisoner's cell.
In the end Anna saved her from getting killed by the evil prince Hans. Elsa was happy in the end, and Jack moved on, and did never return…