Lucia, an active little girl, looses a tooth. Santiago, her out-of-work father, and her overworked but successful architect mother, Pilar, reassure Lucia, by telling her that, that very night, the Hairy Tooth Fairy (a mouse named Perez) will come to collect her tooth, leaving some money in its place. It just so happens that a mouse who had been monitoring the situation tells another mouse, who in turn tells another mouse, until the news fianlly reaches Perez, The Hairy Tooth Fairy. He lives in a boat in the port along with hundreds of other mice who receive the teeth that he collects, and then clean, shape and polish them so that they can be transformed into shiny round pearls.