All In (hardcover) Jennifer Lynn Barnes

After a string of brutal murders in Las Vegas, Cassie Hobbes and the Naturals are called in to investigate. But even with the team's unique profiling talents, these murders seem baffling: unlike many serial killers, this one uses different methods every time. All of the victims were killed in public, yet the killer does not show up on any security feed. And each victim has a string of numbers tattooed on their wrist. Hidden in the numbers is a code-and the closer the Naturals come to unraveling the mystery, the more perilous the case becomes.