Worst Case by James Patterson & Michael Ledwidge.  (Jacket Missing)
One by one, children of New York's wealthiest are taken hostage. But the criminal doesn't crave money or power he only wants to ask the elite if they know the price others pay for their luxurious lifestyles. And if they don't, he corrects their ignorance by killing them. To Detective Michael Bennett it becomes clear that these murders are linked and must be part of a greater, more public demonstration. With the city thrown into chaos, he is forced to team up with FBI agent Emily Parker, and the two set out to capture the killer before he begins his most public lesson,  yet a deadly message for the entire city to witness.