I'm not the first to call Chicago a jungle.— Dresden
Karrin Murphy calls for Harry Dresden's help on the case of Maurice Sandbourne's murder at the Lincoln Park Zoo. All leads point to the culprit being one of the zoo's male gorillas. However, none of the zoo's employees likes the idea; Dr. Reese in particular is vehement in defending the animal. Only Dr. Watson appears quite detached on the topic.
Willamena Rogers joins Dresden in his research before he finds that Dr. Watson is involved in some very dark and powerful magic; which Watson seems to confirm. Dresden and Rogers are attacked twice, once by the zoo's big cats, once by a Hellhound, but Dresden manages to collect a number of clues pointing to Dr. Watson being a hecatean hag in the last stages of preparing for an ascension rite, which she intends to perform in Undertown.
Dresden follows her there; along with her two sisters, the hag is waiting for him, and engages him in battle. Dresden interrupts the rite so that it can't be completed, and the Dr. Watson's hag flees, directed back to the zoo, where she takes Rogers as a hostage. Dresden catches up with them and kills the hag, solving the case.
Karrin Murphy, who counted on him reporting his findings to her, is not pleased, but Dresden feels he will get paid anyway.