Jack Frost awakens from a frozen pond with amnesia. Upon realizing no one can see or hear him, he disappears. Three hundred years later Jack, as the spirit of Winter, enjoys delivering snow days to school kids, but resents that they don’t believe in him. At the North Pole, the Man in the Moon warns Nicholas St. North that Pitch Black is threatening the children of the world with his nightmares. He calls E. Aster Bunnymund, Sandy, and Tooth, to arms. They are then told that Jack Frost has been chosen to be a new Guardian. Jack is unimpressed by this position, as he still resents not being believed in, but North convinces him to aid them.
Visiting Tooth’s world, Jack learns that baby teeth contain childhood memories of the children who lost them; Jack’s teeth are included, but tells Tooth he doesn’t remember. However, Pitch raids Tooth’s home in order to kidnap all of her subordinate tooth fairies except Baby Tooth, whom Jack saved, so that the children’s teeth can’t be collected and steals all the teeth, thus preventing Tooth from sharing Jack’s memories and causing children to not believe in Tooth. In order to thwart Pitch’s plan, the group decides to collect children’s teeth. During their journey, a quarrel between North and Bunnymund awakens a boy, Jamie. Since he still believes, he can see everybody except for Jack. Pitch’s nightmares then attack, provoking Sandy as the Guardian of Dreams. Jack aids, but Sandy is killed by Pitch.