"What?" demanded Mrs. Cook anxiously. She had been very nervous lately. "This postcard," said Mr. Cook. "Listen to what it says. 'Take the advice of one who knows and keep your automobile home at night.'" Bob turned pale. "What does it mean!" inquired Mrs. Cook. "I'm sure I don't know," said her husband. "How is it signed?" "It is not signed at all." "I can't imagine what it's all about," said Mr. Cook. "As far as I know, our car hasn't been out of the garage at night for over a week." "Perhaps Heinrich has had it out," Mrs. Cook suggested. "I'll ask him right after breakfast," said Mr. Cook. "They must have mistaken our car for some one else's." "Who do you suppose sent it?" "I'm sure I don't know," said her husband musingly. "At any rate I think I shall turn it over to the police; I don't like the look of it." Throughout this conversation Bob sat silent. He thought perhaps he could explain part of the mystery to his father, but he was puzzled as to whether he ought to do so or not. On the other hand if his father called in the police, he knew that he and Hugh would have small chance of clearing up the matter themselves. "It worries me so, Robert," exclaimed Mrs. Cook. "I am so afraid that something will happen to you, especially as you are making war supplies at the factory now." "The plant is guarded," said her husband. "Besides I think I owe it to my country to help all I can, don't you?" "Of course, but suppose some of your guards are treacherous." "They are all trusted employees of American birth." "No Germans at all?" "The man in charge at night has parents born in Germany; you know him, Karl Hoffmann, the one who wants to marry Lena. He is just as faithful and true as she is. I can vouch for all the others as well." "He's all right I guess," said Mrs. Cook with a smile. "Even if Heinrich doesn't like him." Heinrich and Karl Hoffmann were rivals for Lena's affections, and they despised each other. Lena, however, seemed to like them both equally well, or at least she did not care enough about either to marry him. Bob used to delight in teasing Heinrich about his rival. When Karl was on the premises Heinrich would sulk in the garage and mutter threats against him. Karl was twice Heinrich's size, but the little blue-eyed, spectacled chauffeur never seemed to question his ability to deal with him. Mr. Cook rose from the table. "I'll go down and ask Heinrich about this car business," he said, "and then I'll go down to the office." He kissed Mrs. Cook and Louise and left the room. Bob followed him out. His father put on his coat and hat and stepped out onto the front porch. A sudden resolution seized Bob. "Father," he said. "What is it, Bob?" asked Mr. Cook, turning to glance at his son. "I think I can explain about the car." "You can?" exclaimed his father in surprise, looking curiously at Bob's pale face. "Yes, sir," said Bob, nervously. "It's a sort of a long story. Shall I tell it all?"