The disloyalty of Furlough refers to his telling on his brother, the literature-loving mouse Despereaux. Despereaux, after having read a story about a Princess and a knight, has followed sweet music to the court of King Philip and Princess Pea. Here he speaks to Princess Pea, with whom he has now fallen in love, despite this action being in violation of mouse law. Furlough tells their father, Lester Tilling, about this infraction and gets Despereaux in trouble. In the meantime, King Philip had Despereaux led away because mice are kin to rats which are outlawed in his kingdom.
The two mouse brothers's father, Lester, decides to call the council of mice, and Furlough leaves to collect his brother for judgment. The council sentences Despereaux to be confined in prison for his violation of the law. Despereaux, however, manages to escape with the help of the jailer whom he has regaled with a story.
Furlough was disloyal to his brother but loyal to the law of the mice, which raises an ethical dilemma.