These two Siamese cats, Koko, a larger and dominant male and YumYum, a smaller and gentler female, are Qwilleran's allies in crime solving and are named after a pair of characters in Gilbert and Sullivan's comic operetta, The Mikado. They are portrayed as having an almost psychic sense of both criminal activity and behavior and of the clues that Qwilleran needs to uncover the truth he's searching for. On the one hand, their perceptions and actions sometimes seem at least unlikely, at most convenient and authorial. On the other hand, the book and the style of its telling fit squarely into the mystery category that grounds its stories in realism only to a certain point. In other words, the focus is on entertainment and the cats are certainly entertaining. On the other hand, however, anyone who has had a cat or indeed a pet of any kind knows how psychic and insightful they can potentially be.