Once upon a time, in the faraway kingdom of Dor, lived a brave and virtuous mouse with comically oversized ears who dreamt of becoming a knight. Banished from his home for having such lofty ambitions, Despereaux sets off on an amazing adventure with his good-hearted rat friend Roscuro, who leads him, at long last, on a very noble quest to rescue an endangered princess and save an entire kingdom from darkness.