A hungry giant is advancing upon the Royal Kingdom, and his evil henchman Slither Slugslime has forced the citizens to give up all their food to satisfy his appetite. Only Tom Thumb, the King's head gardener, will stand up to him, but as punishment Slugslime casts a spell that shrinks him - to the size of a thumb! Mum Thumb, her son Tim, Princess Primrose and her maid Lucy Lastic enlist the help of the beautiful witch Spellena to restore Tom to his normal size. In the meantime Slugslime has taken a liking to Primrose and Mum must somehow rustle up a cake for the giant with two extremely dimwitted sous-chefs.