Eight year old Lucas would like to know how the Tooth Fairy exchanges coins for teeth without getting caught. He is determined to stay awake all night to find out. Meanwhile, a little mouse falls into a trap set by a dishonest contractor who is desperate to tell the world his secret, that the mouse is the Tooth Fairy. Lucas and his family has to do everything in their power to help the sweet little mouse with its mission, which since time immemorial, is to make children happy...