Spring arrives in the Valley of the Moomins, bringing with it the magical hat of the Great and Mighty Moomerlin. Moomin and his friends, Sniff and Snufkin, find it at the top of the hill and take it home.

But when they use it as a trash can, they discover that the little bits of trash they throw inside transform into small soft clouds that they can ride and fly! However, they soon realize that anything (and anyone) that goes inside the Wizard's hat changes form!

And when Moomin puts the hat on his head, he transforms and becomes a different Moomin that no one recognizes.