Slavery
The institution of slavery is ironic. In the United States, people (no matter their status) were guaranteed equal status under the law. However, Black people were not treated as equals simply because of something they couldn't change: their skin color.
Mistreatment
Even though slavemasters buy their slaves so they have help on their plantations. Typically, employers treat their workers—both paid or unpaid—with care and respect so their productivity is increased. However, slavemasters treat their slaves terribly, often beating them and rendering them incapable of working for some time.
Freewater
The Freewater Colony is a place where former slaves go to escape from the doldrums of plantation life (and slavemasters and slave hunters, both of whom are out to get former slaves), despite what Freewater bills itself as the colony is anything but that. The slaves are subjected to terrible mistreatment at the hands of several people.
Homer and Ada
Even though they are young children and not able to fully take care of themselves, Homer and Ada are thrust into dangerous situations through their own actions. They leave their mother behind after escaping the plantation out of necessity; they ironically prosper despite their age in Freewater.
