What shows justice in The City of Ember?

There are different types of justice in the novel The City of Ember. There is a justice system in the city that the characters trust and use; there are authorities and a jail system. However, at one point, the main characters are thrown into jail because they are labelled as fugitives from the law when they discover secrets about a potential exodus from the city.
This shows that the justice system is abused by the leaders, meaning that it is not a true justice system. One of the true forms of justice, however, is the vindication the characters receive at the end. In a form of poetic justice, a power outage (resulting from the crumbling infrastructure because of the misdeeds of prior mayors) allows the characters to escape from prison. They are vindicated in the end when they escape the city and are able to reveal to the citizens what they have learned, in spite of the mayor's attempts to prevent them from doing just that.