In Book the Second, the narrator introduces a rat born in the castle several years before Despereaux. Chiaroscuro—whose name means the arrangement of darkness and light together—differs from other rats, who prefer darkness. One day, Roscuro (as he likes to call himself) nibbles on Gregory’s rope, and the jailer scares him off by lighting a match and burning his whiskers. Since then, Roscuro “showed an abnormal, inordinate interest in illumination of all sorts” (88). He theorizes to his friend Botticelli Remorso that the meaning of life is light. Botticelli is more focused on being a “real rat” (91), which involves activities like torturing prisoners and causing suffering.

Roscuro poises to torture a prisoner, but when the dungeon door opens and the staircase is flooded with light, he is paralyzed with awe: “The rat called Chiaroscuro did not look away. He let the light from the upstairs world enter him and fill him” (93). A soldier throws a red cloth after the prisoner, and Roscuro becomes obsessed with the beauty of it framed against the light. He wants to go upstairs where there is more light, but Botticelli warns him that upstairs is for mice.