This is one of those inspired by true event novels that has been turned into a fictional story, partially because there simply wasn't enough historical information to write it as simply a slightly fictionalized version of history. However, it is true that Mary Bowser was part of Bet Van Lew's spy ring, and in another diary/memoir, her contributions to the cause were singled out by another spy. Beyond that there is not much left in the historical record because Mary Bowser was a black woman in the 19th century, neither of which were exactly documented that well in the past. The story that Leveen imagines certainly rings true as something that could have happened, and is also a very engaging read.
Mary is originally born in Richmond with two slave parents. Though Mary doesn't quite realize this, her parents seem to have a slightly better situation than many other slaves. Her father is allowed to hire himself out for extra money, and her mother and father live in a home together despite having separate owners. Mary's mother works in one of the houses of an affluent Southern family, and their daughter, Bet, is a bit of an oddity in the society - she is unmarried and an abolitionist. Mary is incredibly intelligent for her age, and Bet soon takes an interest in her, eventually arranging for Mary's freedom and sending her to Philadelphia to be educated. They keep this underwraps back in Richmond, though, because Bet also gives Mary's mother her freedom papers, but her mother chooses to stay with her husband until they can possibly buy his freedom. However, if a freed slave stays in the state beyond a certain period of time, their freedom becomes forfeit and they regain their status as slave.
Mary makes a life for herself in Philadelphia and becomes friends with another girl her age at the school, basically becoming part of the family. She eventually even learns of this family's participation as a stop on the Underground Railroad. Despite living in the North, Mary is surrounded by racism and is also unpleasantly surprised by the hierarchy within the black community, often being targeted due to her former slave status. Her mother always believed that God had a higher calling for Mary, and when the Civil War breaks out, her connections in the Underground Railroad give her an opportunity to do more. She returns to Richmond, posing as Bet's slave to gather information, eventually even being hired out to a position at the Confederate's White House.
While the narrative was rather straight forward and simple, I quite enjoyed this novel. Even though much of the story is conjecture rather than reality, it is nice to hear from different voices in history which tend to get lost otherwise. Regardless of how the details actually went, it is an established fact that a freed woman by this name made a significant effort to the war effort. Unfortunately, even now, the narratives that get the most attention are the ones about white people helping, ie The Help. While these certainly have a place as well, they shouldn't be the only ones getting attention.