Finger Lickin' Fifteen by Janet Evanovich (Stephanie Plum #15)

Stephanie's out of the frying pan and into the firing line...Stephanie Plum's tempting mentor Ranger has come to her for help. Someone is trying to destroy his security company from the inside, and he wants her to investigate. On top of that, Stephanie's colleague has just seen two men decapitate a celebrity chef and the unexpected repercussions are more than Stephanie can stomach. But with a million-dollar reward offered for the killers, she may soon be biting off more than she can chew...