The recently-formed private detective agency of (Sherman) Holmes and (John) Garden is going from strength to strength. Holmes invites Garden to a meeting of the Quaker Street Irregulars, a society for die-hard fans of his near-namesake, Conan Doyle's own Sherlock Holmes. Garden is somewhat taken aback by the fervour with which members of the Irregulars defend their opinions on the great fictional consulting detective - but nobody expects a run-of-the-mill disagreement to turn into brutal murder ...