Christopher Quarles is a professor of philosophy and a private consulting detective. Quarles, along with his granddaughter Zena, assists Police Detective Murray Wigan in solving various crimes and mysteries in Victorian England. Whereas the police look for facts and then form a theory of a case, Quarles first forms a theory, often seemingly absurd and based on little more than intuition, then seeks facts in support of it. Of course, to the astonishment of all concerned, Quarles' theories usually prove to be quite right!