Silent Truth by Sherrilyn Kenyon

Hunter Wesley Thornton-Payne III has perfected the role of bored playboy. When he attends a fundraiser for the Renaissance Women's Center hosted by Chicago's elite, intending to pick up information about a dangerous organization - he first has to find and terminate an assassin who is killing innocent Americans connected to an upcoming arms trade agreement.

Abbie Blanton's mother falls prey to a mysterious illness, and Abbie turns to her investigative skills as a television news journalist. While attending a Chicago fundraiser, she leaves with more questions than she arrived with, and becomes the focus of a killer with a twisted sense of honor. As if her night hadn't gone badly enough, Abbie encountered a man she never forgot...and never wanted to see again. Abbie begins to realize Hunter isn't the superficial playboy he appears to be - but a dangerous operative with a tortured past whose success depends on destroying the best chance her mother has to survive.