In Evil's Service

Robin Ellacott receives a mysterious package via courier — inside which she discovers a severed female leg.
Her boss, private detective Cormoran Strike, is less surprised but no less alarmed. From his past, there are four possible candidates for the sender's identity — and each of the four is capable of unimaginable cruelty.
The police focus their efforts on finding one of these four, but Strike becomes increasingly convinced that this particular suspect is innocent. Together with Robin, they are forced to take the case into their own hands and delve into the depths of the distorted psyches of the other three suspects. But the mysterious killer strikes again, and Strike and Robin realize their time is running out...
"Career of Evil" is a devilishly gripping mystery novel with many unexpected plot twists, as well as a story of a man and a woman at a crossroads both professionally and in their personal relationships.