Being a tale of a mouse who falls in love with a princess, a rat who craves the light, and a half-deaf servant girl who wants to be a princess.
It starts with the mouse Despereaux and his oddities from birth onward, and how he reads a book instead of eating, and how he hears, as he thinks, honey and tracks it down to the music the king makes for his daughter -- and then flashes back to how Roscuro (short for Chiaroscruro, which his parents thought was funny because rats hate light) talked with a prisoner and stole the red tablecloth he had sold his daughter for, and how he went up into the castle one day and what happened -- and how Miggory Sow, the servant girl, had been sold to a man, and gotten clouts on the ear for every failure until her ears were cauliflowers and mostly deaf, and how she saw a princess one day, and when the king outlawed soup, the soldier who announced it discovered she was a slave and brought her to the castle instead. . . .
All of which inspire a plot, and then a daring rescue, which involves a jailor who ties a rope to his ankle, a suit of armor with no one inside, a cook who cooks soup though it's against the law and wants to feed it to someone, a broken heart that heals wrong, and much more.