Series numeration from www.goodreads.com.

Sequel to: Labyrinth.

"A young wife is forced to confront a decades-old deadly secret when a medium connects her to her dead grandfather. A vicious psychopath wants ultimate revenge against Savich, but first, she wants to destroy what he loves most-his family. A series of three red boxes are delivered personally to Savich at the Hoover Building, each one containing puzzle pieces of a town only FBI agent Pippa Cinelli recognizes. Savich sends in Cinelli to investigate undercover but someone knows who she is. Savich and Sherlock are up to their eyebrows in danger, but can they figure out the red box puzzle and the young wife's secret before it's too late?"