V myshinom semeystve, obitayushchem v starinnom korolevskom zamke, rodilsya myshonok po imeni Despero. V otlichiye ot svoikh sorodichey on obladal khrabrym i blagorodnym serdtsem, a yeshcho lyubil chitat' i slushat' muzyku. Odnazhdy on uvidel printsessu Goroshinku i vlyubilsya v neyo. A kogda kovarnyye krysy khitrost'yu zamanili printsessu v mrachnoye podzemel'ye, Despero, slovno rytsar' v siyayushchikh dospekhakh, spas yeyo ot vernoy gibeli.