When Lucia loses a tooth, her father recounts to her the story of a peculiar tooth fairy that is actually a mouse called Pérez, who keeps children's teeth and turns them into diamonds. When Pérez, is kidnapped, Lucia embarks on an adventure to save him.
As Pérez continues to collect the teeth of children which they keep under their pillows, he goes to steal Lucas' teeth, but when he arrives, he realizes that the child is still awake, upon which the events take an unexpected turn when Pérez falls asleep inside Lucas' house.