Showing The Watchman by Robert Crais

A long time ago, Joe Pike asked for help. In return, he would, one day, be called upon to return the favour, no questions asked. That day has come.

Joe Pike is asked to protect the life of Larkin Conner Barkley, a spoiled rich girl who happens to be a federal witness in a major case. But someone is leaking information about their whereabouts, and the killers are getting all too close. So Pike hatches a plan: disappear into the anonymous underbelly of Los Angeles, turn the tables, and hunt down the hunters.

Enlisting the help of Elvis Cole, Pike uncovers a web of lies and betrayals; even the cops aren't who they seem. But as the body count rises, it becomes clear that Pike's biggest threat may be the girl herself - an edgy, yet intensely vulnerable soul determined to destroy herself, unless Joe can fill the void in her bruised heart.