Pickax is preparing for its sesquicentennial celebration, and in the midst of all the family reunions, the Siamese super-sleuth Koko smells trouble. One evening Koko pounces down on the head of the wealthy Ledfields' obnoxious nephew, and when the Ledfields fall ill, Jim Qwilleran begins to think that Koko's behavior is more forewarning than feline frolicking.