The most important geographic area is New York City at the time of the American Revolution.
Not everyone was sympathetic to slaves in the North, including in New York. During the American Revolution, slavery was already a hot topic. This is why there are compromises in the constitution, such as making slaves count as 3/5 of a person and having some slave states and some free states. Which state and city you lived in also mattered.
The owners have little sympathy for their slaves. An example is when Isabel is crying over her own mother’s grave, and Robert Lockton treats her roughly.
He released me with a shove and pointed to the cemetery where they buried white people. “Go pray for her that owned you, girl.” (ch 1, p. 7)
Isabel’s new owners, the Locktons, are worse. They pretend to be Patriots, but are really Loyalists. They are spies.
Even though the Lockton family are Loyalists, but Isabel sees a chance for herself in the American Revolution. Some of the revolutionaries do not want slavery. New York City is in the middle, not terribly North or South. Not everyone feels the same way.
The British capture New York in September, 1776, and Isabel escapes in Janary of 1777. Even after escaping, things are not perfect. There is still a war going on, and slavery would not be outlawed for years to come.