The first day of class for graduate students Ian Joyce and Sarah Gold starts like any other --- until a fellow student, Jake Havens, pulls a wrinkled envelope from his backpack. Inside is a bloodstained scrap of shirt from a boy murdered 14 years ago and an anonymous note taking credit for the killing. The only problem is that the alleged murderer is already dead. Suddenly, the class has a new assignment: find the real killer.

Michael Kelly is back and racing to save Chicago from a deadly new foe: a biological weapon unleashed in the city’s subway system.