Nightshade by Michael Connelly

Stilwell was working for the LA sheriff's department when he got "exiled" to Catalina Island. But it turned out that he liked his job there. He met a girl named Tash and life was good. Until the body of a woman with a purple streak in her hair turned up. The cops on the mainland want to take over the case but Stilwell wants to keep it and when they're ordered to work together, he keeps following his own leads. 

The more he finds out about the dead woman with the streak of nightshade purple in her hair, the more he begins to piece together a theory of who might have killed her. But he has to find proof. Then Tash gets kidnapped.

It's an engrossing story in an interesting setting. And I'm wondering if it's the beginning of a new series, now that Harry Bosch is basically retired and in poor health.Another winner from Michael Connelly.