The Shakedown. The Brandon Hall Series, #6

Hall is approached by a marketing executive, asking him to check in on the man's son, who has been acting strange as of late. Though it initially looks like a boring case marked by possible infidelities, the case quickly spirals out of control, and they soon realize there is more than meets the eye. As Hall and Charlotte investigate, several dead bodies pop up, and they are aided by the mysterious James Rankin, who has his own reasons for helping.