Watchman by Robert Crais (2007)

Joe Pike, an ex-cop, ex-Marine, ex-mercenary, is coerced into protecting Larkin Barkley, a hard-partying young heiress whose life is in danger after becoming a hunted witness in a secret federal investigation. “With the help of private investigator Elvis Cole, Pike uncovers a web of lies and betrayals. As the body count rises, Pike;s biggest threat might come from the girl herself, a lost soul in the CIty of Angels, determined to destroy herself unless Joe Pike can teach her the value of life … and love.”