THIS was an excellent mystery / bit of a thriller! The author was inspired by a real woman, Kate Warne, one of our nation's first women private detectives.
Follow the fictional story of Nell, who tags along with Warne as her (entirely fictional) orphaned nephew. Nell watches Warne develop her detective skills and helps with several cases, before ending up involved in Warne's efforts to protect Abraham Lincoln on his train ride to his Inaugural Address.
The author, Kate Hannigan, offers a fantastic, ELA Common Core standards based lesson plan for 5th grade (with two 6th grade Common Core standards), touching on slavery and the Underground Railroad, as well as the lesson materials necessary to teach it, and a few discussion questions of her own.