Folded Paper Mystery

Nick Peters was a repairer of watches, sole proprietor of a little store in Fourth Street-a strange little man, a bit of a philosopher too, and fond of friendly arguments with Fin Corveth, a free-lance journalist. One day Peters is murdered, and Corveth finds himself involved in a baffling mystery in which a little brass ball plays an important part-for the little brass ball conceals an emerald locket, which in turn conceals a blank square of folded paper, which obviously holds a secret . . . but what?