Then the door burst open and Herman von Essen rushed into the room, bristling, panting. He stopped, glared at the little group, and pointed a trembling finger at Hildegarde. "There you are.... I had you watched. I knew you would come here.... It is like you, disgracing yourself. Have you no brains? Rushing here to this man that has made your name common in the whole city.... Out of here, out of here while I attend to him!" He advanced threateningly, but Hildegarde did not move, only eyed him with level contempt. "You," he raved at Potter, "you entice my daughter!... By God! I'll show you!..." He advanced again, burly fists doubled, Bismarck-like face purple and distorted by rage. At the instant when it seemed the furious German would rush upon Potter, Cantor took one step forward and spoke. His voice was incisive, cold, compelling. It cut through von Essen's rage to his consciousness and halted him. "Von Essen," said Cantor, "you forget yourself." That was all. He stood very straight, heels together, shoulders squared--the attitude of an officer facing his company. Von Essen stopped, and his rage dropped from him as if it had been some false face which could flutter to the ground. He was _compelled_. Cantor's cool voice had a surprising, a powerful effect. "I--" he faltered, seeming to grow smaller of stature, to wilt. "You will take your daughter home," said Cantor, still in that cool, commanding voice, "and you will treat her as a gentleman treats a lady. Am I understood?" Von Essen nodded. He was inarticulate. "See to it," Cantor said. "Miss von Essen." He bowed to Hildegarde, and, walking to the door, held it open for her, standing cold and straight while she passed her father and came toward him. Von Essen followed. He had the appearance of a man suddenly caved in. Hildegarde paused in the door and turned. "I can't ask you to pardon him," she said. "I shall come again." Then she preceded her father through the door. Cantor closed it and smiled grimly. "You need have no anxiety over Miss von Essen," he said. Potter shook his head. "That gets me," he said. "How do you do it, Cantor? In another minute I'd have had to thrash that old bounder.... I'm much obliged for the miracle." "He needs a little taking down," Cantor said, contemptuously. "These rich German-Americans get too cocky sometimes. They have to be shown." "I'd like to have your formula," said Potter. Cantor changed the subject. "How's the motor coming?" "Slowly." "I haven't seen the drawings," Cantor suggested. "I'm interested, you know." "I'd like to show them to you," Potter replied, "but I'm not showing them to anybody. I feel as if it were government work, you know. I'm sure you'll understand." "Perfectly. I shouldn't have suggested it.... Just dropped in to ask you to come down to the club to dinner to-night." "Thanks. I'll show up early. Want a game of handball and a shower? Take me on?"