December Rain

Genealogy and a treasure hunt can lead to... murder.
The day had darkened, and when two children at the library hide under a table during a storm, they overhear something more ominous than the rumbling outside. Strangers talking about stealing treasure.
What, exactly, had the children heard?
Soon, people are murdered, and the connections start to become more defined between a centuries-old secret kept by a former slave and the killings happening today. But what was that secret and what are the connections between the people who were attacked?
Sidney Lake knows he can help. Intrigued by research, he and Tillie James are the perfect pair to look into Lowcountry family connections and try to put the pieces of this puzzle together.
But the clock is ticking and this is no simple puzzle. More people will die if they don't find answers soon. Sidney and Tillie quickly discover that family is complicated, and some connections are more dangerous than others.