Wait! You don’t know of the story? Really? Oh, c’mon, everybody has heard of the story of Frosty. Fine, fine, I’ll tell you, don’t get your knickers in a bunch. I’ll start from the beginning. Meanwhile, why don’t you fix yourself a nice little cup of hot chocolate with some of them tiny little marshmallows, okay?
One day in a school shortly before Christmas, a magician named Professor Hinkle is hired to perform for the pupils but fails to entertain them, so instead the children go outside and build a snowman, who they name Frosty. However, Professor Hinkle's rabbit, Hocus Pocus, escapes from the building while wearing his owner's top hat, which the children decide to put on top of Frosty's head. To their surprise the magic of the hat causes Frosty to come to life with a trademark exclamation: “Happy Birthday!”
This delights the students, but after seeing that the hat is actually magic, after harboring some initial doubts, the agitated Hinkle wants it back. The children refuse to turn it over to him, much to his annoyance. Antagonized by both the children's dislike of his magic performance and the fact that he may not receive his top hat back, Professor Hinkle makes it his main priority to snatch the hat back from Frosty. The children and their snowman gleefully parade through town, shocking passersby with Frosty's anthropomorphism. The children are very happy with their new friend, but the temperature is rising and Frosty must leave for somewhere that is colder or else he will melt!
Karen, a little girl who is especially attached to Frosty, suggests that the group bring him to the North Pole, but they are barred from boarding a train that will take him there due to their lack of money for tickets. So, Karen and Frosty sneak into the back of a train delivering frozen goods, and off they go. However, Hinkle has also secretly managed to hitch a ride on the train as well in hopes of stealing back his hat; but soon, he accidentally falls off and is knocked cold.
Needing to put as much distance between themselves and Hinkle as possible, Frosty and Karen continue on toward the North Pole, accompanied by Hocus, who has chosen to side with them rather than Hinkle. While Frosty is safe from melting, Karen is freezing and Hocus, seeing her predicament, gathers with a group of woodland creatures to build a fire for her. Frosty knows that it is best if Karen is brought home, and he and Hocus decide to enlist the help of Santa Claus to transport her there.
Frosty carries Karen inside where she would be warm and safe, however, that proves to be a lethal move for him. Hinkle has followed them on foot all the way down the hill to the greenhouse, huffing and puffing, he slams the door, locking Frosty and Karen inside, and saying “As soon as Frosty melts, the hat will be mine!”
In the meantime, Hocus manages to bring Santa back to the greenhouse in order to take Karen home. But when they enter in they discover to their horror Karen sobbing over a puddle of water that used to be Frosty, with Frosty's top hat lying nearby. To console Karen, Santa tells her that Frosty was made of Christmas snow and can never melt away - that is, as soon as a crisp December wind kisses it, Frosty will be back just as before.
But Karen is still inconsolable, so to prove his point, Santa opens the door and a cold, strong gale blows through the greenhouse. And the puddle of water becomes Frosty once again (but is lifeless at this point because he is not wearing the hat). Karen is just about to put the magic hat on his head when Hinkle pops up, declaring that it's his and he wants it back. Santa stands up to him and threatens to never deliver another present to Hinkle in all his life if the magician dares to harm Frosty in any way and doesn’t let Frosty have his magic hat.
Santa tells Hinkle that even if he wants a CHANCE for a Christmas present this year, as an act of penance, he must write a hundred zillion times, promising to never try to hurt the snowman again. Then Santa tells Hinkle that he'll find a new hat in his stocking on Christmas morning. Now joyful, Hinkle runs off to fulfill this order. As soon as the magician leaves Frosty is brought back to life (with another cheerful “Happy Birthday!” declaration) much to Karen's joy.
Afterwards, Santa takes Karen and Frosty on a sleigh ride back to her house. There Frosty and Karen bid each other goodbye and Santa brings Frosty back to the North Pole, keeping his promise that Frosty will be back again someday.
And he did keep that promise!
Even a snowman knows the value of his word.