When he left Graydon Bansemer on the sidewalk in front of the office building, he swung off with his long strides towards the Wells Street bridge. His brain had laid aside everything that had occupied its attention during office hours and had given itself over to the project that hastened his steps homeward. His supper that night was a small one and hurriedly eaten in order that he might get to work on his new device. Droom grinned and cackled to himself all alone up there in the lamplight, for he was perfecting an "invention" by which the honest citizen could successfully put to rout the "hold-up" man that has made Chicago famous. Elias Droom's inventive genius unfailingly led him toward devices that could inflict pain and discomfiture. His plan to get the better of the wretched, hard-working hold-up man was unique, if not entirely practical. He was constructing the models for two little bulbs, made of rubber and lined with a material that would resist the effects of an acid, no matter how powerful. On one end of each bulb, which was capable of holding at least an ounce of liquid, there was a thin syringe attachment, also proof against acids. These little bulbs were made so that they could be held in the palm of the hand. By squeezing them suddenly a liquid could be shot from the tube with considerable force. The bulbs were to contain vitriol. When the hold-up man gave the command to "hold up your hands," the victim had only to squeeze the bulb as the hands went up, and, if accurately aimed, the miscreant would get the stream of the deadly vitriolic fluid in his eyes and--here endeth the first lesson. Experience alone could do the rest. Young Bansemer hurried to their apartments on the North Side. He found his father dressed and ready to go out to dinner. "Well, how was everything to-day?" asked James Bansemer from his easy chair in the library. Graydon threw his hat and gloves on the table. "Terribly dull market, governor," he said. "It's been that way for a week. How are you feeling?" "Fit to dine with a queen," answered the older man, with a smile. "How soon can you dress for dinner, Gray?" "That depends on who is giving the dinner." "Some people you like. I found the note here when I came in a little after five. We have an hour in which to get over there. Can you be ready?" "Do you go security for the affair?" asked Graydon. "Certainly. You have been there, my boy, and I've not heard you complain." "You mean over at---" "Yes, that's where I mean," said the other, breaking in quietly. "I think I can be ready in ten minutes, father." While he was dressing, his father sat alone and stared reflectively at the small blue gas blaze in the grate. A dark, grim smile unconsciously came over his face, the inspiration of a triumphant joy. Twice he read the dainty note that met him on his return from the office.