"You have one rare faculty, Jones. You can, when you choose, sharpen the pencil of your mind to a very fine point. Specialize, my boy, specialize."

Adrian Van Reypen Egerton Jones —"Average," to his friends—has spent the five years since graduation from college "specializing in life," indulging his wanderlust and living comfortably on twenty-five thousand a year. In order to inherit the millions that his late uncle has bequeathed, Average must spend five continuous years as a resident of New York City. Already bored, he is advised by his friends Waldemar and Bertram to take up a hobby. Waldemar, a newspaper owner, suggests that he become an "Ad-Visor"—someone who investigates classified ads on behalf of clients to root out swindlers.

As his college professor had opined, Jones possesses a particular singularity of focus, which allows him to notice details that others miss. In the process of investigating unusual and downright bizarre advertisements, he stumbles into solving actual crimes—and he finds he was born to it. Why would someone advertise for a musician to play a B-flat trombone in a certain street at a specific time of day? Or offer an unusually large reward for information about the death of a bulldog? What can be the meaning of a message written entirely in pinpricks? Who is the man who speaks only in Latin? These and other tantalizing puzzles will leave the reader eager to spend more time with the decidedly not-Average Jones.