Dead Witch Walking (Kim Harrison)

Rachel is a witch, working with the law-enforcement agency that governs supernatural creatures like warlocks and weres, but her boss hates her and has been deliberately sabotaging her work to make her ineffective, so she quits to go start a new agency with her friend the vampire and colleague the pixie. This means breaking her contract, so naturally they hire assassins to kill her. At that point I'm already confused by the plot. Why does her boss want her to fail, when it seems like he'd want his unit to be successful? And why spend a lot of money and effort to kill her for quitting? And then Rachel decides her only course of action is to take on the most powerful criminal mastermind in the city, figuring that if she brings in the proof that he's running drugs they'll have to - what? Take her back? Cancel the contract on her life? I'm even more lost. Then the whole book is about her doing one ill-considered thing after another in an attempt to bring this guy to justice, so that he's out to get her, or at least get her to work for him (??), and at the end she does get the proof she needs to bring him down, and uses it to blackmail him into leaving her alone instead of turning him in. ???? There's a lot to like in this first book of a series. Rachel's voice is fun, and the world in which humans have an uneasy relationship with the supernatural is an interesting one, but the plot just had me scratching my head. Sorry, but it didn't work for me.