Horn of Plenty in Bloomington, MN

How does Mac Hollingsworth, a French Horn player in the Navy Band, become involved in a plot to deploy a bioweapon? Where did it come from? What is the intended target? And what can she possibly do to prevent its deployment?
Mac discovers something unusual one day while cleaning her horn and is suddenly "reassigned." A woman she doesn't know is killed while driving Mac's car. Someone keeps trying to kill her. And she finds herself working with people who are not who they seem.