Kate Warne's assistant

Lately I've been reading a fictional book, intended for kids, called The Detective's Assistant. The author Kate Hannigan invents a young orphaned niece of Kate Warne, who comes to live with her aunt in Chicago and gradually participates in Pinkerton cases. I recognize many of the cases from Allan Pinkerton's books such as "The Expressman and the Detective" though the cases are slightly altered to allow the teenaged Nell Warne to participate in disguise. She gets to meet not only Allan Pinkerton, but also George Bangs, Timothy Webster, and Hattie Lawton.

Along with the detective cases, there is a mystery as to why Kate Warne's husband Matthew Warne died back in Chemung County, New York. Kate thinks it was a murder by Matthew's brother (and Nell's father) Cornelius, and that was the reason she left her home in New York. Nell Warne says that the death was a tragic accident, though she's not certain of all the details, being a kid at the time and only overhearing what adults said about the death. But Nell strongly defends her father and decides to investigate by writing letters to her friend Jemma in Canada. Jemma's family are free blacks, but they had to leave New York because slave hunters came to the area and weren't picky about capturing true slaves or not. Jemma and Nell write to each other in ciphers about the Underground Railroad, and discuss how to find Jemma's father, whom they call The Maple Tree.

Anyway, the story culminates in Nell solving the mystery of Matthew's death, making up with her aunt Kate, and helping to secretly smuggle Abraham Lincoln to Washington DC, while avoiding an assassination attempt. It's a fairly readable book, and not too dumbed down for adults to enjoy; I did find it unrealistic sometimes for Nell to be disguised as full grown men when she was supposedly only 13, but I guess I've seen tall teenagers that age. The Author's Note at the end explains the historical vs fictional elements of the book, and Hannigan mentions all the research she did to write the story. She apparently even found a source in Kate Warne's own words! I was disappointed to read that Robert Pinkerton shut down the detective agency's female department in 1876, apparently while Allan Pinkerton was still alive. However, Allan may have been somewhat incapacitated still by his stroke in 1869. What a rotten thing for Robert to do, and I wonder what William Pinkerton's opinion was.