Produced by Darleen Dove, Mary Meehan, and the Online Distributed Proofreading Team at http://www.pgdp.net. This file was produced from images generously made available by The Internet Archive/American Libraries. By PAUL AND MABEL THORNE _Authors of "The Sheridan Road Mystery"_ NEW YORK DODD, MEAD AND COMPANY 1922 COPYRIGHT, 1922 BY DODD, MEAD AND COMPANY, INC. THE PLIMPTON PRESS, NORWOOD, MASS PRINTED IN THE UNITED STATES OF AMERICA CONTENTS CHAPTER I—THE TOLL IS EXACTED CHAPTER II—"FRIENDS OF THE POOR" CHAPTER III—ENGINEERING-CRIMINOLOGY CHAPTER IV—THE CAR IN THE FOG CHAPTER V—THE HAUNTED TREE CHAPTER VI—THE FLAMING HAND CHAPTER VII—SPIRIT CLUES CHAPTER VIII—THE GIRL ON THE HORSE CHAPTER IX—LUCY CHAPTER X—CROSSED THEORIES CHAPTER XI—TELEPHONE CALLS CHAPTER XII—SATURDAY CHAPTER XIII—A PUZZLING WARNING CHAPTER XIV—THE INTRUDERS CHAPTER XV—THE MASK OF DEATH CHAPTER XVI—THE FATAL DANCE CHAPTER XVII—AT THE DOORSTEP CHAPTER XVIII—TRIANGULATION CHAPTER XIX—FACE TO FACE CHAPTER XX—THE INVISIBLE DETECTIVE THE SECRET TOLL CHAPTER I—THE TOLL IS EXACTED "I’m damned if I give up a cent! I’ll die first!" "You very likely will. Others have. To refuse these people is the first step toward suicide." "But are the police so impotent that a gang like this one can operate unmolested right under their very noses?" "The police are efficient in ordinary cases. These people, however, operate mysteriously. So far, the police have been helpless." The two men who thus discussed a criminal clique which was extorting money from prominent and wealthy citizens were seated in an exclusive Michigan Avenue club. From their deeply upholstered leather chairs they looked out across the busy street, with its hundreds of automobiles and strolling pedestrians, to the green lawns and leafing trees of Grant Park, awakened into renewed life by the soft breezes and warm sunshine of early June. To the first speaker, Robert Forrester, lately returned from army service in Europe, and familiar with the privations, struggles and horrors of the great war, it seemed ridiculous that a band of criminals could endanger life in the heart of this bustling, crowded, well-policed city. Yet the threat was in his hand, and his older and presumably wiser companion assured him that they could make good the threat.