I. THE MYSTERY OF THE “SYBARITE” 1
II. THE SECRET SERVICE 15
III. THE CABARET DANCER 31
IV. THE BURGLAR’S MICROPHONE 44
V. THE WHITE LIGHT CAFÉ 55
VI. THE POISON GAS 69
VII. THE DIVORCE DETECTIVE 80
VIII. THE PULMOTOR 97
IX. THE TRAILING OF PAQUITA 109
X. THE DETECTAPHONE DETECTOR 124
XI. THE FRAME-UP 135
XII. THE EAVESDROPPERS 149
XIII. THE SERPENT’S TOOTH 160
XIV. THE GEOPHONE 171
XV. THE NIGHT OF TERROR 183
XVI. THE INVISIBLE INK 196
XVII. THE CIPHER LETTER 211
XVIII. THE RADIO DETECTIVE 226
XIX. THE WIRELESS WIRETAPPER 242
XX. THE SPEED DEMON 256
XXI. THE SUBMARINE EAR 270
XXII. THE TELAUTOMATON 285
XXIII. THE CURB MARKET 300
XXIV. THE PHANTOM CIRCUIT 315
XXV. THE ADVENTURESS 329